You can block out specific dates for a mechanic. For example, when they're on holiday or otherwise unavailable, so no bookings can be made for them on those days.
Steps
Go to Availability > Mechanic Availability.
Use the selector at the top of the page to choose the mechanic you want to edit.
In the calendar, click on the date you want to block out.
Toggle the Disabled switch on for that date.
The date will now show as "No bookings allowed on this date," and it will appear in the Overrides section towards the bottom of the page, where you can review or remove it at any time.
Notes
Overrides are only shown for future dates, the current day, or the past month (30 days).
To remove a holiday or override, find the date under Overrides and click Remove.