You have to have a a Microsoft Rewards account first.
http://rewards.xbox.com/mymissions/
"Well, here’s a weird thing that Microsoft is doing. If gamers with an Xbox Live Rewards account pick up Halo: The Master Chief Collection this December, Microsoft will toss them 15,000 points. Those points can be turned in for a $15 account credit.
This isn’t applicable to the early adopters who bought The Master Chief Collection on or near launch. That’s problematic because the game, quite frankly, still doesn’t work as it should. The multiplayer matchmaking, while slowly improving, has been an absolute mess since launch. Those first few days, the game was entirely unplayable online.
343 Industries has promised to make things right for early adopters, but this $15 credit for gamers picking the title up this month only isn’t sitting well with those who’ve been annoyed by The Master Chief Collection since early November."
You're Gonna Carry That Weight.
Xbox One - PS4 - Wii U - PC