1) When you archive an assignment that has already been completed in one of your classes, it will move from the "Due Soon" tab at the top of the page, down to the archived tab which is labeled by the month and the year.
2) In your class, under the "Assignments" tab, scroll down and click on the "Month, Year" tab and you will see your archived videos from that month. Students will still have access to the videos that have been archived, it will just allow your "My Classes" view to be organized more clearly by the date the assignments were due.
3) If you would like to unarchive your videos, on the far right there is a button with an arrow that you can click on to unarchive the content. (Here's a picture so you can see it).
Once you unarchive it, it will move the assignment back up to your "Due Soon" section!