If you would like to restore a User, Course or Lesson that you have previously archived (meaning not permanently deleted) you may do so from the archive page. 

Visit the archive page and over there you will be able to view all users/courses/lessons that exist in your archive. You can restore an item by clicking on the restore operation in the operations column (1).

When you do so, a pop-up window will appear to you for the restore confirmation. Click to restore the item (2) and when you do so this item will again be available in your system.