If a student is accidentally removed from a course, can they be retrieved including any assignments they have uploaded?
Good news! If you (or a Canvas admin, if you don't have access yourself) restore the student's enrollment, their submissions, grades, discussion posts, etc., will be restored.
Try this (and contact your Canvas admins if you don;t have the permission to do so yourself): How do I add users to a course?
Retrieving data ...