First log onto the platform.
Select "My events"
Then you will land on your events page select the tab "Upcoming events" then select the "Manage" link for the event you want to cancel off.
Under "Booked Photographers" you can select the cancel button next to your name. This will notify the event organiser that you can no longer attend the event. You may also want to send the organiser a courtesy text message especially if it is short notice so they can make further arrangements and to confirm they received the cancellation email.
Do remember that event organisers and participants are relying on photographers to cover the day and to give as much notice as possible when cancelling.