How to change booking dates for a guest

Hi there I am trying to change the arrival date to one day earlier and the platform is not allowing me to and the guest has tried and also not allowing him to.


Booking number ***


He would like to arrive on 23 March instead of 24 March for 2 nights please assist!!


I tell the guest that they must contact booking.com if they want to modify their booking (since we are not allowed to do that on their behalf).