If you’re unable to make it to a job that you’ve claimed, you can remove it without any penalty up to 48 hours in advance. Within 48 hours, though, and you may be subject to a late cancellation fee.
Learn how to remove a job here.
Note that professionals cannot reschedule a job on behalf of the customer. You are only able to remove yourself from a job. Furthermore, you should remove yourself as soon as you know you won’t be able to make it, in order to avoid a late cancellation fee.