If you are the organizer or have administrative privileges, you will be able to click on the button View Attendees to see the list of attendees (see article “How do I view who is coming to my event and contact them?”). From the attendees list, you can use the action buttons on each attendee to check them in, mark them as a no-show, remove them from the attendee list, or clear the “Attended” or “No show” flags, if marked incorrectly. 

Note, to do live event check-in, use this view on a laptop, tablet, or mobile phone. Or, update the event record post-event with check-in data collected at the event.