If you want to stop online bookings but still allow internal bookings there are two ways:
1) Create a Periodic Close out
Follow this guide on Periodic Close Outs (Recurring)
2) Exception Date
In Settings > Restaurant Details > Other Details > Booking and you can add an exception date:
Add in your dates
Click Create Exception
Remember to save at the bottom of the page!
You can also remove them by pressing the x next to the date.