In order to enable or disable bookig cancellation at online check-in platform go to Property Settings / Online Guest Account / Settings and choose the Enable / Disable option for Cancel reservations option:

If Cancel reservations in enabled the guest will have the possibilty to cancel the whole booking:

You can also enable or disable the cancelling particular nights option.

In this case the guest will be able to cancel perticular nights, however in case the Cancel reservations option is disabled he won't be able to cancell all the nigts: