Answer call requests by pressing M-key
From Zenitel Wiki
A call request is normally answered by pressing a dedicated DAK key programmed to dial the answer code 7638. However, it is also possible to answer call requests by pressing M-key. In this way the operation will be the same as for direct calls in private ringing mode.
From the Exchange & System window choose the Events button:
In the Event Actions window click the Insert button and create an event with the Control Room station as the event owner, and the following properties: