You can cancel a 1:1 appointment or a class attendee.
To cancel an appointment:
Click on the appointment to view the appointment details
In the upper right corner click on the "..." menu in the upper right
Click "Cancel"
Confirm cancellation and select whether or not to send the cancellation automations
Canceling an attendee in a class works similarly. First click on the class to view all attendees, then select the attendee to cancel, then click on then "..." menu for the attendee and select cancel.
Canceling an entire class is possible by selecting the class, choosing the "..." menu, then selecting "Delete". The cancellation automations will be sent when canceling all attendees for a class.