Expired Promotional Credits

It seems this isn't possible. According to https://aws.amazon.com/awscredits/

10. Promotional Credit is valid for a limited time only and cannot be redeemed after the expiration date indicated .... Failure to redeem Promotional Credit before its expiration date will result in its forfeiture .... No refunds will be granted for any expired or cancelled Promotional Credit.

This doesn't make any distinction between credits acquired through APN, and from any other sources.

If you have a contact within APN you may want to check with them. Or try raising a billing support case https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/billing-get-answers.html#billing-support