If there are specific dates or periods where you do not operate you can exclude these from being booked by your customers. This is called "Blackout Dates" and is available from the Schedules screen.
Screen showing navigation to Management > Schedules.
To activate a Blackout Date or range for any Schedule click on the Schedule Name to access the details for the Schedule. Here's an example;
Click on Blackout Dates and you will see a screen like the one below;
In this example, April 1-3 2020 are excluded from the schedule. This blocks the range of dates from being booked by both customers and through your internal booking screens. NOTE - it's important to blackout all available timings from the Schedule for the tour or journey you wish to close.
That's it. Now your customer won't be able to book on April 1-3 for this Tour/Journey.