I'd do a number of things.
1. Current Virtual Console Subscription: Expand the VC subscription service to include GB, GBA, and N64 ASAP. Figure out timelines on those and announce the schedule for when they are expected. Prioritize just getting them out, adding online gaming to the games could be done as a later update. I'd also rebrand this back to being called the Virtual Console.
2. Future Virtual Console Subscription: Beyond just expanding the VC service, I'd start preparing to make it a general service not tied to Nintendo systems to be launched with the launch of the next system. This netflix-like service that you can play on a variety of devices would build upon the Switch's VC sub service, so it would launch with GB, GBA, NES, SNES, N64, and GC libraries.
3. Hardware issues: I'd make sure the joycon drift issue got solved immediately and all new joycons being shipped by start of 2021 were the updated model. I'd also make the connection between the system and the joycons a bit sturdier (as recently my left joycon gets disconnected and i have to fidget with it for a few seconds to reconnect) and build that into all newly shipped systems by start of 2021.
4. Switch 2: I'd be setting up a straight upgrade to the Switch as the next gen system, to launch likely in 2024, though certainly if the teams had already come up with interesting new features I'd evaluate those for inclusion. I'd be targeting power benchmarks a bit stronger than the base PS4/XB1 models, 1080p screen, 512 GB disk space, built in bluetooth, do, make the form factor slightly larger to accommodate extra batteries and slightly larger 2nd gen joycons.
5. More Switch models: I'd make sure a "Switch Plus" was in development with an expected launch date of Fall 2021 or Spring 2022, depending on Switch sales next year. The launch would coincide with a price drop of the current models to $180 and $240. This model would be same form factor as the original, but with larger screen, slightly more power in order to improve resolution and/or frame rate of games that don't already run optimally, larger storage space to probably 256gb, a sleeker dock, a stronger kickstand, and built in bluetooth. I'd also be get internal research done about the market viability of a "Switch Home" model, to launch Fall 2022, same specs as the Switch Plus, comes with a Pro controller, priced same as Switch Lite.
6. Online: I'd direct the company into modern times with a revamped online play setup. Friend codes gone, messaging included, voice chat included. Just in general take a much more consumer friendly and modern approach to online gaming. As soon as we had the plan figured out I'd make a public announcement of the future revamped online setup coming to the Switch. No more need for phone apps to do stuff the Switch should be doing itself - also speaking of this, the Switch gaming log would get a big update with more detailed playtimes and stats and graphs and stuff.
7. Studio moves:
Sega - I'd look into purchasing Sega, and have them focus on making modern versions of their best franchises, and put some trusted Nintendo project managers in charge of their teams to make sure quality is up to Nintendo standards. I'd also then add the Genesis to the VC service, with the Master System, Saturn, and Dreamcast to be added later to the 2nd gen VC subscription service once it goes platform independent.
Game Freak - I'd do whatever needed to be done to greatly improve the quality of Pokemon games. The series rests on its laurels, I'd be intent on giving it a BotW style revolutionary treatment. What form that would take I don't know, but Pokemon needs a revamp.
8. Third parties: I'd be talking to Capcom about making a version of the next MH from the ground up for the Switch to be released same day as the other versions. I'd be talking to Square-Enix about Kingdom Hearts and the next Dragon Quest to get ground up versions of those with same day releases as other versions. I'd regularly focus time on getting more third party big games to the Switch, and setting up relationships where at the very least they have a bunch of AAA PS4/Xbox1 straight ports launching on the Switch 2 in year one, as well as versions of next gen games made for Switch 2.
9. Game Pricing: I'd put in place a standard pricing model of $40 for ports of games like DKC:TF, NSMBUD, etc rather than the $60 price tag as if they are new games. Mario Kart wouldn't apply because as sales have shown the market has accepted it as the Mario Kart for the Switch and not just an old game. Also little party type games like 1-2 Switch would be priced at $30 on launch. Also I'd start the Nintendo Selects collection on Switch for first party games whose sales have slowed down. Nintendo Selects would be priced at $30, while ports that launched (or should have launched at $40 under the new pricing rules) would go down to $20. Nintendo Selects would immediately include Pokemon Let's Go, Arms, Mario Tennis, Xenoblade 2, Kirby, Yoshi, DKC: TF, Captain Toad, and Link's Awakening off the top of my head (probably a few more).
10. Mobile - I'd focus more attention on the mobile market, looking to put out a couple games a year. The main difference from Nintendo's past efforts would be smart monetization strategies instead of terrible ones.
11. First party software:
a) I'd make sure the fact that Nintendo studios are consolidated to a single system actually improves the output of games. I'd make sure portable or lapsed or degraded series like Fzero, Golden Sun, Advance Wars, Kid Icarus, Mario Strikers, Warioware, Excitebike, Wave Race, Mario & Luigi or Mario RPG, Star Fox, and more are all being worked on and in the case of something like Star Fox which is more degraded than lapsed, I'd focus attention on going back to the drawing board to revise the series for success.
b) I'd be getting a Switch Sports game (in the vein of Wii Sports) with online play out on the Switch no later than holiday 2021, and it would include among other things improved and deeper versions of Bowling, Boxing, Golf, and Tennis from Wii Sports (sorry, Baseball).
c) I'd release several HD collections of big series including Mario (64, Sunshine, Galaxy 1+2 - assuming this isn't already planned this Fall), Zelda (OoT, MM, WW, SS), Metroid Prime Trilogy but I assume this is already coming.
d) I'd direct Ring Fit to become an annual series of different genres of fitness games so people who bought the Ring can actually take advantage of it beyond a one-off game. These games priced without the Ring would be $40 each. Possible games to look into would be a mini game collection, fighting, action, shoot 'em up. Some of these games would be multiplayer with 2 or more rings. Instead of having one(or two)-off fitness products like Wii Fit & Wii Fit Plus, and Ring Fit, I'd developer Nintendo's fitness games into a brand, in which Nintendo is considered THE fitness gaming company.
e) I'd make sure Switch is getting another 3D Mario, another Mario Party, and a brand new 2D Mario game is being built for the Switch, something entirely different than the "New" series.
f) I'd get MK8D a paid DLC with two new cups and a few new items added specifically for those courses.
g) I'd make a couple new internal studios to make Bit Collection games or something like that. The idea being go after the retro and indie feel with Nintendo's big IP. Retro indies in general already harken back to the NES/SNES days, so this would be the same thing but with actual Nintendo games. These games would be cheap to make, would allow experimentation on the franchises, while also giving players a nostalgic taste of NES/SNES games. Priced at $30. These games would go for the old school feel of tight controls, solid difficulty, 2D with 8/16-bit style focus. This could almost be looked at the handheld side of things in previous gens when the main big games would come to Ninty's home system and smaller games would come to the handheld - except more experimentation in the indie vein would be the goal here. This would of course also include later IP that weren't around back in the 8/16-bit days.
12. Next gen first party software: I'd focus Mario Kart 9 and Smash on the Switch 2 to rework their formula. Smash Ultimate was, well, ultimate, and that series as it has been has run its course. Mario Kart as well feels stale. Both series would get big changes while still keeping true to their concepts. Mario Kart would go more a Smash route of including courses and characters and items of a range of Nintendo games (which, granted, MK8 just barely started with some non-Mario courses). Smash I'm not sure what direction it would go in, but some sort of changes are needed because you can't top Ultimate by doing just the same thing.
cue, take over world!