How to report stay change to Booking.com?

In case the guest has already checked in and they would like to extend or shorten their stay, you can report this change to Booking.com along with the new price. Your guest will receive new confirmation email with updated information immediately.

According to Booking.com, the following bookings cannot be modified:

The reservation is a Smart Flex Reservation
The payment is made using Payments by Booking.com
The reservation is marked as a double-booking

Reservations that are made for more than one property (with the same dates) cannot be requested to change.

Go to Guest Planner and click on a booking you would like to report. This booking opens in the Big Card view.
Click Booking actions and select Report stay change.
Select the new departure date. After the date is changed, you can also edit the prices.
Click Save.
The confirmation screen is displayed. Click OK.

The booking will be updated in Rentals United and Booking.com systems. Your guest will receive new confirmation email with updated information immediately.