It can always occur a class needs to be cancelled. When opening your profile on the web https://www.getmatchable.com/account/ you can view all your bookings. 

However, in order to cancel a class you would always need to get in touch with the trainer. As only the trainer can cancel your participation.

How to contact the trainer?

Select your Training you would like to cancel > Contact Venue > And a new page will open with the contact details.