Admins can un-archive both teacher and admins user accounts in Assist.

Step 1: 
Click on users

Step 2: Enter the details in the dialogue box to search the user

Step 5: Under status, change to archived

Step 3: Select the user you wish to un-archive by clicking on the select box

Step 4: Click on un-archive button on the right hand side of the screen 

Your user shall be un-archived.