Modify dates of reservation 3259913811

Dear partners,

The client of the reservation n°3259913811 wants to change the dates of his stay from June 7th-10th, to June 6th - 9th.

We want to accept his request and we already changed the reservation in our internal system to be sure he'll have the 3 rooms he booked. However, when I try to click on "Modify dates of stay" on his reservation, it seems that I can't modify for these dates. Can you help us regularize the situation please ?