In case you have inadvertently placed a request, you can delete it by tapping the menu icon (3 dots) at the right side of the request and choosing 'Delete request'. Please note that your credit will only be refunded if the request has not been answered yet.
There's no need to delete requests if they are not getting answered. Unanswered requests will be refunded automatically after the flight has departed. Requests will not be answered quicker if you delete and re-post it.