Closing registration for a future Zoom Meeting.

I am trying to close registration for a future Zoom Meeting and I am not finding the option to do so. Since my meeting capacity is 300, the only option I have is to enter a number of 300 or less to stop further registration. I currently have over 700 registrants and I want to close it now so that on the date of the meeting, the first 300 joining will gain access. I do not want to deny any of the 700 registrants prior to the date of the meeting but rather approve them all now and then allow the first 300 entry.