To change the date format in the room search/booking form, please open the WordPress Customizer and navigate to “Rooms” > “Search/Booking Form” > find the option: “Date Format“.
Considering the width limit of the form input box, the date format in the forms only supports numeric format.
Date Format on Cart & Checkout Page
To change the date format on the Cart & Checkout page, please navigate to “Settings” > “General” > “Date Format“.