How to reset a date in an availability calendar

Old states are not stored, so really resetting a state is not possible. But, of course, you can overwrite any state - and set it to any state you want (*) - by editing the entity the calendar belongs to, selecting the "old" state, the day(s) had and selecting the period of the cancellation.

(*) this is configurable in the fields instance setings, so check these, if you can only select 1 or a few states.

Does this answer your question?

same problem.

Force CSS

.acbf-date .form-reset {
display: inline-block !important;

This looks different. When end-users want to change the dates they have selected on the calendar they can use the reset dates button. the basic styling that comes with the calendar might not be sufficient for all themes, so yes, custom styling on top of that is expected.

IMO, the OP was asking about people (house-owners) who want to cancel a booking, ie, make these dates available again. As the data of availabiity calendars is not revisioned, even not if the entity is revisioned, that is only possible by changing the states of the days manually to the states they had before.

Ok fietserwin thanks for the quick answer.

it is not possible even with the rules? Ie giving a maximum limit of reservation and disable the day?

I' m lost, can you give a description of your situation and what you want to accomplish?