Now it is only possible to cancel an event registration after an attendee has signed in at the portal front end or an event manager can cancel the subscription in the event registration section in the markting app.

It possible to customize the customer journey with a customer channel activity and a flow.

Not very easy out of the box solution is available

Other event applications have the possibility to put a cancel button in the event e-mail. When you send it to the attendee they click on this button and automatically the event registration is canceled for this person for the specific event.