Restrict who can book a specific class, using membership tags. To do this:
Create a membership tag
Click Customers > Tags > Add new tag > select Membership tag
Assign the tag to a membership
Click Memberships > Subscriptions and packs > select a membership > edit details > scroll to Tags section and select the tag to assign
Update a class to only take bookings from this tag
From customers with this membership tag -- click Classes > Upcoming Classes (or create a new one) > select a class > click Actions > Edit class > Scroll to the bottom
In Additional Settings select 'Restrict who is eligible to book'.
Toggle on Restrict bookings to customers with specific tags & choose which membership tags to restrict bookings to > then Save