@Bene383
Changing a reservation can only be done/accepted if the reservation has not ended and if shortened, it must be completed before first check-in time on the new checkout-date.
As a host you can also make the change, giving you the opportunity to also amend the precalculated price (which is based on refund policy attached) in the change form , to be sure the 2 nights are refunded.
If reservations has ended, you can only refund them money via resolution centre.
Please note: vandalism on their car is not your responsibility,assuming it was parked in a public space. Interupting a stay can also be a case for the guests Travel Insurrance ?