webiner

When creating a new Zoom Webinar one of the options is "Registration      [   ] Required". If you check this box then registration is required for everybody in order to attend. If you wish to remove the requirement of registration, you can simply uncheck this box.

If your question happens to be... how to enable entry without the registration requirement while a Webinar is in-session?

There is not a way to avoid the registration requirement for a new attendee.