You can send a message in the thread for the request inviting the guest to resubmit the request, they will be able to do so and then you can accept the new one.  

Or you can contact us right away and we'll change the status of the request for you.  Then return to their request message and add a reply with a note to let them know you changed your mind and that you've asked us to update the status. Until we do, they won't have your address and phone number and you won't have theirs, so you may want to exchange that information if the visit is today or tomorrow.