Block days on the website:
Go to My profile and select Block Days.
Choose the ads you want to change availability for.
Click the purple button labeled "Select dates".
Mark the days in the calendar when the item is not available for rental.
Click "Save".
Alternatively:
You can also block days directly from a specific listing:
Go to "Listings" and select the ad you want to block.
Click "Blocked Days" in the box that appears.
Note that you can only block days for one listing at a time using this method.
Block days on mobile website or in app:
Go to your profile and select "Block days".
Select all the ads you wish to block the days for.
Click the purple button saying "Select dates" where you then select the days from the calendar view.
Mark the days in the calendar.
Click "Save".