The Leave button is used to return to the alarm processing queue without actually ending the event, allowing another operator to pick up the event as normal. This is done by clicking the “Leave” button in the top right corner of the screen.
When leaving the event you have the option to "Park" it for a specified length of time. If you Park the event that event will be put on hold and be added to the "Parked" tab, instead of going back to the main queue.
Operators can re-open the event by going to the Parked tab and clicking it as normal. Alternatively when the parked time expires the event will automatically be escalated back to the main queue.