Previous versions of assessments can be viewed in the Assessment Version History screen. Assessments listed there include those that have an Archived status.
Archived assessments can be restored from this screen:
Hover over Assessments in the menu and select Assessment Version History from the submenu.
Choose the Assessment Type and Assessment from the fields at the top of the screen.
The grid will populate with all versions of this assessment.
To restore an archived assessment version, click the Restore button (to the right of the selection).
This will update the assessment status to Shelved.