Restoring missing enrollments
When a course is concluded, all people in the course are separately concluded. Currently, unconcluding the course does not automatically restore the enrollments. They will need to be restored separately.
View more information about unconcluding a Canvas course.
If you are an instructor or student, contact a Canvas administrator for your school.
Confirm Concluded Enrollments
To confirm that the user(s) are concluded in the course, in Course Navigation, click the People link. Then click the More Options icon  and select the View Prior Enrollments option .
This will show you all concluded users in the course.
If you go to the user details for each of the users, you can restore their enrollments.
You can also re-invite or re-import the users with an Active status to the course to restore them.