refund customer

I am new to booking.com and trying to setup my property. By mistake I made it open for booking while the room is not ready, but a guest happened to search my listing and paid for one night at midnight (While I set the check in time is 3 pm~5 pm). Could anyone let me know how to deal with this situation? How to refund the guest? 

Ismini Karali

You can ask him to cancel his reservation and you will waive the fees.