Ideally, you would make that day available in your "working hours/availability" in your MeetFox account and then create a Google/Microsoft calendar event to block the day every 2nd week. Make sure you set your event to 'busy' to allow us to detect that you are unavailable.
In case you haven't integrated with Google or Outlook, you can add a meeting into your MeetFox calendar to appear as unavailable. This can be done in the 'Calendar' tab under your 'Profile'
We will also developing certain customizations for each service in the near future and have added this to our roadmap.