There are many topics discussing this. You can visit the user’s profile page and change it but they’ll still need to verify their address, which is almost always a good idea.
If you want to take matters into your own hands, you can do it from the rails console. It’s much safer than direct database queries.
This might work
u=User.find_by_username("pat")
UserEmail.find_by(user_id: u.id).first.update (email: "pat@gmail.com")