If you have archived a course and need to restore it to use it again, you can easily do so from the Training Admin Workspace. To restore an archived course, head to this workspace and select Manage Training -> Courses on the left panel. Set the Status Archived to get a list of all Archived courses.
Select the course you want to restore. Under the Course Panel, select Unarchive Course.
Please note: the progress of the users that were enrolled in this course before archiving it will appear as it was before the archival. However, the course will not be restored as part of the learning paths that it was a part of before archiving it.