Hi Al!
If I'm understanding the question right, all you would need to do is select the session you wish to close, click "edit" and about halfway down the page under the "Status & Capacity" section, select "No" under Allow Registration. You can also turn off registration in Attendee Hub if you are using that or Event App. Then save and close!
------------------------------
Tori Martinez
Event Technology Specialist
Creative Group Inc.
United States
------------------------------