To open room availability, go to Property > Rates and Availability, search for the desired period in the Date field, and click Filter.
To close the availability day by day, go to the desired room and date and select the availability conditions Closed - OTAs or Closed - hqbookings or both conditions. And at the end of the room type list click on Save, see example:
Now to open availability for multiples dates at once, click on Long Term Definition > Availability define the period select the new room types and in the options Arrival Closed, Departure Closed, Closed - OTAs , Closed - hqbookings select NO, add a new line using the + Add button and open the availability for the other room, do this procedure for the types of rooms you want to open. See example:
Don't forget to synchronize your changes!
If your property is connected to the channel manager, always make changes accessing the menu Rates and Availability and synchronize the desired period through the Synchronize Rates and Availability button so that the rules are sent to the OTAs that are selling the rooms online.