My iphone has an Apple ID that I don't recognise
I have an iphone 7 with ios 15.5, and I've noticed that under Settings, the phone has the wrong Apple icloud ID. It says the ID is a gmail email address that is similar to my non-gmail email address (which is my usual Apple ID), but I've never had a gmail account! Of course I can't sign in to make any changes, because I don't know the password.
My wife purchased a new iphone yesterday, and I wonder if the guy at the Apple Store might have accidentally reset our account using an Apple ID that looks like ours, but isn't?
Thanks in advance for any helpful suggestions.
iPhone 7