I want to change the date to another day because I can't come on the scheduled date.

ゲスト予約:Guest Reservations 外部サイト予約(一休.com/Expedia等):Booking site reservations(Ikyu.com Expedia and more) オーナー予約:Owner Reservations ギフト予約:Gift Reservations DAO利用:DAOReservations

Please cancel the reservation you already made and make a new reservation for a different date.

Please check this article for the cancellation method.