Once a Zoom meeting has begun, if the meeting needs to have a waiting room, the host can update the setting within the meeting.
The host will need to click the Security button on the Zoom Video Window Interface
At the top is the option to Enable Waiting Room
Once the Waiting Room is enabled, if a participant joins, the host will be notified
and they can allow them access into the meeting
Or view the list which will display both the waiting room attendees as well as the participants within the meeting
The host or co-host can send a message to all attendees in the waiting room to communicate without admitting them into the meeting.
Alternatively, if a participant needs to be removed or returned to the waiting room, the host and co-host can do this by opening up the Participants button and click the more button then select Put in Waiting Room
If the user wishes to have a waiting room enabled ahead of the meeting, they can update the settings within the Zoom portal to reflect that change on that meeting.
Navigate to their meetings page within Zoom
Edit the meeting and under the Security section check the waiting room