Instructors have their own student account that is connected to their instructor account. You access this via "Take my courses" or via the dropdown to "switch to Student". When you are logged in as a student, go to your profile (your name at top right) and then to login data. There you will see your student login ID. It might be listed as "InstructrorXXXXX" x= a number. You can change that to your own email address which is obviously easier to remember. Then you can login with that email address to the courses app.