On the game page there will be a tab that says "Game Details". Right to the right of that it will say "Add game". Scroll over "Add game" and then click "My games" when it comes up. There you go.
Nintendo still doomed?
Feel free to add me on 3DS or Switch! (PM me if you do ^-^)
Nintendo ID: Mako91 3DS code: 4167-4543-6089