If you purchased the AMD GPU Card before 09/30/2019 you are out of luck.
Here is AMD's Terms & Conditions for Radeon Raise the Game Bundle (Choice of 1 Game Offer) - COMPONENT AND SYSTEM INTEGRATOR (SI)
If you just found out about the Promotion than it was just lousy luck on your part that you purchased the qualifying GPU card BEFORE the AMD Campaign even started.
If you want you can always open a AMD REWARDS SUPPORT ticket and see what they recommend from here: Support - AMD Rewards .
But most likely they probably will say that you are not eligible since you purchased the GPU card before 09/30/2019. But no harm in asking.
But you do seems to qualify for another AMD Campaign that started on 07/01/2019: AMD Radeon & Ryzen with Xbox Game Pass for PC - Component and System Integrator Campaign
See if the Retailer where you purchased the GPU card is eligible for the AMD CAMPAIGN. If they are they are the ones that needs to send you a Coupon. If you didn't receive one open a AMD REWARDS SUPPORT Ticket from the link above and ask them what you can do to get the Coupon and redeem it at AMD REWARDS website.
NOTE: I have attached the AMD Terms & Conditions to this post for you to download and read for yourself in case you are interested.
