How do I enable / disable public profile for attendees?

Attendees can enable / disable their public profile on their own from their dashboard.

However, if you wish to enable their profile from the backend, you can go to Contacts, click on attendee's name and on the next page, set the option "Enable public profile" to Yes.

Alternatively, you can use the Bulk Edit feature under Contacts to enable public profile for up to 30 attendees at once. Repeat the process for the next 320 attendees and so on.