Hi @PeterLentz ,
Thank you for posting on the Instructure Community!
As a Free-For Teacher user, you do not have the ability to delete student's email addresses, as that is an admin-only function that is not provided under free for teacher, as you only have access to course settings, not full instance account settings.
That being said, since it appears your students will be using their school-provided email addresses, I strongly recommend that you reach out to Instructure Support and explain what happened, and to request that they delete your student's accounts so they're able to re-enroll with the same school-provided email address for their canvas accounts. Staff at Instructure are the admins of the free-for teacher Canvas instance, and they would be the ones to help you with that.
I hope this helps point you in the right direction! Please feel free to reach out with any additional questions or concerns.
Best,
Noah