Changing to booking dates

There is no such possibility in the theme. You can manually reserve these three days so that no one can book on these days

>> Acutally i cannot do it, as we have minimum limit of 7 days and i cannot change it because it is mandatory.

I meant manual reservation (see screenshot). There are no restrictions on the minimum number of days.

The rest of the order parameters can be changed only by canceling the old booking and creating a new one via frontend.