Mentors can block-out dates by visiting the Calendar's Available Hours tab. Scroll down past the Global availability settings to find the block out dates section.
Blockout dates set are automatically applied across all existing sessions.
Another method for setting blockout dates is through the session settings. Here's a step-by-step on how to do this:
Visit the Calendar page.
Click on the small gear icon on the upper-right-hand side of the session card.
Click on Edit Session
This will then open the option to update session settings.
Click the edit icon next to When are you available?
Click on the Blockout Dates section
The option to add blockout dates will appear. All blockout dates added will be applied across all existing sessions.