Need to clear old AP aging/AP balance but leave expense details in order to accommodate an unearned revenue vendor credit

We have an old outstanding AP balance comprising 3 months of healthcare premiums where the vendor issued an unsolicited large credit that they just confirmed yesterday is valid. As we were unsure if the surprise credit provided us would be revoked by the vendor, we conservatively allowed the outstanding AP balance to remain until the credit issued was resolved. We now need to eliminate the AP but need to retain all prior expenses posted to create the AP balance as they're legitimate healthcare premiums incurred and were already allocated to numerous grants currently closed. Currently, the aged AP detail needs to be cleared and the AP balance needs to be reclassed to likely an unearned revenue account. We'll ignore that this is a prior period adjustment for now, but this may come into play with the auditor. I'm new to QB and don't know if we can do a JE to reclass the AP overall balance (for the unsolicited credit provided) to Unearned Revenue and then issue some kind of vendor record credit(s) to clear the AP Aging listing/detail.