sorry if my late. I discover how to trigger this event like 10 seconds ago while playing the map.
Remember the hole where's ratman? Look up, there's like a piece of broken concrete on the ceiling, break that part and break the other piece of concrete, once you go up there will be (what I think) is the Admin Room, on the desktop buttons more precisely the one on the left on the front desk, it's the button to activate the event.