In the A/P module, go to Check Printing, Manual Processing and the check can then be deleted and the invoice will be showing as not paid.  You will need to open the December general ledger transaction entry module for this change to post.  If the bank account has already been reconciled and the check is showing outstanding, it will need to be deleted there also.

Thank you very much for the quick response.  We have not yet reconciled the bank account for December so that will not be an issue. 

I just want to be sure there are no additional steps due to having closed AP for 2025 already?

There shouldn't be.  You can still access all the invoices and payments as long as you didn't select them for deletion when you did the year end close.

Thank you very much for your help!