Method 1:  General Users

In Mazevo go to: 

1. Events
2. My Events
3. Click on the Event to be Cancelled
4. Click on Cancel Event
5. If prompted enter Cancel Reason

Method 2:  Admins

In Mazevo go to: 

1. Events
2. Find Events
3. What > All Events for a Contact > First Name Last Name
4. When> Enter desired date range
5. Click on the Event
6. On Books Tab, check the box on the Row
7. Change Bookings
8. New Status > Cancelled
9. Enter Cancel Reason

See also:  https://www.gomazevo.com/help/how-to-change-the-status-of-a-booking