You can change the way your rooms will be assigned by going to Settings -> Booking form -> General options for booking form -> Room Assignment.
The settings will be applied wherever the bookings come from (channels / homepage).
There are four different options:
- Optimize (reduces gaps if possible)
- Based on unit number/name in ascending order.
- Based on unit number/name in descending order.
- Random (avoids having some rooms being overused)