A person is away
Open that person under Team. Time off & vacations is where you block a stretch just for them. Enter a start and an end, then Add. Their services are unavailable then, and everyone else keeps taking bookings.
The whole business is closed
On Schedule → Availability, Add blocked time closes a date or a stretch of hours. Your weekly hours stay as they are.
Already booked
Time off and blocked time do not cancel existing appointments. Check those dates and contact those customers yourself.