Hi Hock Lin
Welcome to Microsoft Community.
Based on your description, I understand that you received a winning reward email for the GitHub Copilot Hackathon, but there was no coupon code, and I know exactly how you feel!
Until then, congratulations my friend, you must be an awesome technologist.
Although I'm just a tech support person not part of the relevant team, I seem to have found a way to contact the corresponding team.
You can open the page in the link and click on it according to the image below, at which point you can send an email to the manager of the Github Copilot hackathon.
I sincerely hope that you will be able to get your loot soon after contacting the correct department!
I would also be more than happy to discuss the technical side of things with you if the opportunity arises.
Best Regards
Arthur Sheng | Microsoft Community Support Specialist