If a student has not started a course, you can unassign it and return it to your pool of course keys. Go to Manage Courses. Select the course that the student is taking from the list. Select the Track Students tab and you’ll be able to see your students’ progress.
If the student hasn’t started the course, you’ll see a trash can symbol. Select this icon and it will remove the course from that student. The course will return to your available pool to assign. You can follow this same process for Unassigned Course Keys by selecting that option from the Course Management page. You can remove any Course Key that has a trash can symbol and return it to your pool of available Course Keys.