OTA's only know the number of rooms of a 'Type' that are free on any given date.
They do not know which specific rooms are free.
In our hotel below, Rooms 101 and 09 are both configured as 'Single' rooms. One has a booking on Saturday, one has a booking on Sunday.
OTA's see that there is one Single room free on Saturday, and one also free on Sunday, and will accept a two night booking. (This is not related to any channel manager, the same would be true if you were manually updating your availability at the OTA's side.)
When the booking is imported into Caterbook, it is assigned to those two free rooms.
In this case, we can move one of the bookings onto the shuffle row - note this DOES NOT RELEASE AVAILABILITY TO THE OTA's.
And edit the two night booking:
Firstly by removing the second 'room',
and then by extending the first room to two nights, remembering to change the price of this room.
Finally we move the booking from the shuffle row into the free room on the calendar.
Sometimes, it may not be possible to use the shuffle row in this way due to the range of longer stays within that particular room type.
You might wish to discuss with the guest that there might be a need to change them into a different room type, or, explain that they would have to move rooms after a particular number of nights.