Managing event registrations is available for Producer+ and Enterprise licenses and allows you to view all of your registrations, and disable access to those who you do not want to be able to view your event.
Log into your account, navigate to your event and click into your specific session
Click on manage registrations which appears on the left hand side of the page
Once you have clicked on manage registrations a list will appear with all registrants for the specific event. You can filter these by their first letter of their surname, alternatively you can press show all
Once you have found a registrant that you do not want to have access to your event, you untick the access enabled button, this will remove that users ability to join the event.