Where did you change the mail id? from browser? If so, please try from Visual studio and see if that fixes this. Please check similar thread: https://learn.microsoft.com/en-us/answers/questions/219477/logic-app-can-not-change-mail-id
Meanwhile, I just tried to replicate, by switching between two gmail ids. It works as expected.
Just make sure the intended connection is selected from the designer as below? Please let us know if you have issues even after you have changed the connection.