Hi @Norma614
Just to clarify... what are the dates of the original reservation and what change has the guest requested? Sounds like the date of the original checkin is in August, but they wish to arrive tomorrow?
If that is the scenario, you may have to try modifying the reservation as the Host and a message will be sent to the guest to accept. Have the guest withdraw/cancel the reservation alteration. Be sure you don't have any restrictions set on your listing page that would prevent the change, like you have a block for preparation day, min stay, don't accept same day reservations etc. Any calendar limitation you have set could prevent the change. If you need to change those settings to get the alteration through, I would turn OFF instant book before you make those changes. Then process the change of reservation and have the guest accept. Then you can turn Instant Book back on. Whew! Thats alot. You can always contact CS to help you figure this out as well.
Let us know how it goes!