Here are the Terms & Conditons for your AMD Promotion:
Basically the Retailer where you purchased the AMD 5800X MUST GIVE YOU A GAME CODE OR COUPON to redeem at AMD REWARDS website.
If they are participating, then they should have either sent you an Email with the Game Code or Coupon or giving you some sort of documents with the Game Code or Coupon.
AMD doesn't provide Game Codes nor Coupons only the Retailer/Vendor where you purchased the AMD Processor will have to supply you with the Game Code or Coupon.
If they ARE PARTICIPATING and you didn't get a Game Code or Coupon than you need to talk with the Retailer's Customer Service to find out why.