Go to the 'Benefits' tab and select Redeem in the Azure sponsorship benefits section. Use your Azure subscription email when redeeming credits.
After redeeming go to the Azure portal and confirm if you in the correct directory. See: https://learn.microsoft.com/en-us/azure/cost-management-billing/troubleshoot-subscription/no-subscriptions-found
Also note that The Azure Pass Sponsorship offer can't be combined with other licensing, prepaid, or credit offers (i.e Microsoft Enterprise Agreement, Cloud Solution Partner, Azure in Open, Azure Pass, Action Pack, etc.).
If this has been done and you still cant see it, you may need to create a billing ticket:
https://azure.microsoft.com/en-us/support/create-ticket
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola