If you have a user that has been granted Primary or Place Admin permissions*, other Primary Admins have the ability to downgrade these users to Staff only.
To do this:
Navigate to the Staff list in the Web App
Select the user you would like to downgrade by click on their name
Click on 'Revoke Admin Permissions'
This will now change the user to Staff.
If they were a Primary Admin, and you would still like them to be a Place Admin, you can now select 'Invite as Admin'.
*Note: Learn more about Staff Permissions.