Hi Alan and Ben, thanks for the question and referral.
To un-archive a design, from the Designs page, there is a switch for Active and Archived designs (top left) to select the files to view. Choose Archived Designs to display the list of archives. Select the design you want to un-archive. This expands the slide-out details panel on the right. Click the Un-Archive button on the details panel. The design is unarchived and moved to the Active Designs view (change from Archived Designs view using the switch top left).
The best place to start with WorksManager queries would be the page. There is an introduction video from the release of the archive feature. Archive Design Feature Introduction linked in the June 10 release Notes followed by a clarification of what archive means in the July 2 release Notes.
The FAQ under has a few items also.
Hope this helps