Swap Primary and Parked Domains

I host a number of sites that years ago dropped their original domain names for ones that had been originally just parked alternate domains. (E.g. the alternate domain was shorter and they realized the primary domain wasn't all that useful.) Though those domains have long since expired, they are still in the system as the primary domain, resulting in AutoSSL errors, etc. If I try to alter the account to switch the primary domain, it complains that the new domain already exists in the system (since it was originally parked as an alternate domain on the account). What is the cleanest way to fix this? Do I need to delete the parked domain and then change the primary domain? Or is there a better way to handle this? Thanks!