If your event has a limited capacity, attendees who attempt to join after the maximum capacity has been reached will automatically be placed on a waitlist. Waitlisted participants are added in chronological order, and as spots become available, they will be admitted accordingly.
Organizers can edit attendees even when event is at full capacity from the “Edit Attendees” section. There you can change people from “Invited” to “Attending” or “On Waitlist”.
If your event have a pre-event survey, here's the list of requirements