Click on the "Calendar" tab on the menu on the left side of your dashboard.

Click anywhere in the calendar that you wish to make available for bookings. A side menu will pop out from the right side of the screen. Here you can select "Availability" .

You can select the date that you wish to be available by clicking on "Scheduled date". You can then select the start time and end time you wish to set yourself available.

Once you have selected the date and times you wish to be available, click "Create".

This will create your one-off available time slot.