To amend your availability for a particular location:
Go to your Calendar
Click on the day you wish to edit
Select the locations you wish to update your availability for
Select all the dates you wish to edit your availability for
Select the times that you wish to set yourself as available for. When the time is displayed in purple, indicates it has been selected
Press save
Note - This will override the default availability that has been added to your location for the dates selected
To edit your default availability, see article: How do I set my default availability for a location?