You are able to block the time for your staff member in case that they are unavailable.
Go to "Calendar">>"Staff Calendar".
Click on "Add Block Time".
Here you can add block time for particular staff member.
3. After choosing the date, staff, start and end time, mention a reasons, and click on SAVE.
Note: After adding a block time admin will not be able to book any appointment under that particular staff member.
Additionally, for your reference, below is the video tutorial.