@Inger-Marie0 If the dishwasher was not listed as an amenity, then the guest is not due any refund. They may go to Airbnb in an attempt to obtain one anyway. Airbnb CS reps are (astoundingly) not super competent and aware of policies, so the guest may be successful. You may therefore want to get ahead of the guest and contact Airbnb yourself to explain the situation. Once a refund has been given to the guest, you’re pretty much out of any chance of having it reversed.
By the way, here is the guest refund policy,
https://www.airbnb.ca/help/article/2868/airbnb-guest-refund-policy