@Susanna328 Good grief, what a load of trouble already, and the stay hasn’t even begun. Direct the guest to cancel, since they can’t make the dates they booked, and then block them so they can’t try to rebook new dates.
You’re never under any obligation to accept a request to change dates. If you do, it’s a good idea to stipulate that it’s a one time only courtesy.
If the guest won’t cancel, and is instead angling to take advantage of your good will for another date change, then I suppose you’ll have to wait for airbnb, to help you with a penalty free cancellation. You could cancel it yourself, but you’ll be penalized and the dates blocked.