Hi @WinnieBell !
I apologize for my late response.
I just wanted to clarify: are you trying to edit your students email on the same account they originally had? If so, with free for teacher, it isn't possible to do that since you have to be a canvas admin to make changes, and that permission is only available to Instructure employees.
What I recommend instead to minimize issues (and if you don't need any of the grades or data from your students existing account) would be to have them sign up and register with their new email address. If for some reason their email does not seem to exist when you go to add them, hop onto your course settings and scroll down and enable Let students self-enroll by sharing with them a secret URL or code. From there, refresh your page and provide your student with the registration URL. They should be able to be added to your course, as long as their account registration is complete, without any issues.
Let me know if this helps!
Noah