This is a previous thread I answered that has the Terms & Conditions for the AMD Promotion: how to redeem game from my 3700x . It is attached to my reply.
Download it and see if Singapore participates in the AMD Promotion. Or call Amazon Customer Service and ask them if Amazon in Singapore participates in the AMD Promotion.
Or you can simply open a AMD Rewards Support ticket and ask them yourself if Amazon Singapore participates in the AMD Promotion from here: Support - AMD Rewards
EDIT: went to Amazon.sg and looked up Ryzen 7 3800X and it doesn't indicate anywhere about the AMD Promotion. Usually this indicates that it doesn't participate in the promotion. Otherwise it would have posted the AMD Promotion on the webpage like Amazon USA did. But best to validate it at AMD REWARDS SUPPORT to be certain.
No mention about AMD Promotion further down the webpage or anywhere on the webpage.
Amazon in the USA does mention the AMD Promotion: https://www.amazon.com/AMD-Ryzen-3800X-16-Thread-Processor/dp/B07SXMZLPJ but for the XboxX Game Coupon only.
Further down the page at Amazon USA:
