@Catherine2638 Anything you change on your listing, be it price, cancellation policy, available amenities, availability settings, house rules, whatever, only affects future bookings. Confirmed bookings are locked in to the original conditions.
If you had kitchen facilities listed when a guest booked, and later removed them, the guest would have a legitimate complaint and would be owed a refund or discount. If you add an amenity that wasn't available when the guest booked and let them have access to it anyway, seems like a guest would be pleasantly surprised.