Navigate to the Technician Detail screen for the technician you'd like to turn off access to
Click the checkmark next to "Active" (located below Name and User Name)
>>> You'll now see the checkmark removed from the active box
Click Update at the bottom of the screen.
>>> You will now be directed back to the Technician Listing screen where you will see a green success bar at the top of the screen indicating the update was successful. You will also see "false" in the "Active" tab next to technician's name indicating the technician is no longer active in the system.