Q: one of my emails was inadvertently assigned an apple id is there a way to undo this

On a macbook pro one of my email addresses (xxxx.gmail.com) was assigned an apple id inadvertently, Can this be rectified so the email can be used with my real apple id

My macbook pro is running el capitan latest version

When going into messages preferences when I try to add (xxxx.gmail.com) to be used says is already used with another apple id. Is there a way to rectify this so email will not be associated with this apple id