Apple ID email changed

We accidentally changed my daughter’s Apple ID email and verified it. Now she has an email address that is not hers as the default email address for her Apple account. I added her previous email address (the correct address) as an alias Apple ID, but there is no way to change the default email address back to the original. If you try and delete the incorrect email address it asks for a new email address that cannot be linked to an existing ID. When you enter the previous email it says this address already exists. Apple support had no idea how to correct this problem. It seems you can change emails or add an alias very easy, but you cannot revert the email address to a previous one which makes no sense. You should be able to change the ID address in the profile which seems like a simple task. Anyone have this issue?