Event organizers set their own cancellation policies. They are usually included in the terms&conditions. You can find them right next to the "send request" button before sending an application or under "Contract&Payment" if have already sent you application.
If the terms look ok to you and you would like to cancel, you can do so by clicking the "Cancel Request" button in your dashboard. Please note that this means you are requesting a cancellation. The organizer will then cancel your application according to the agreed terms.