As a host or co-host, you can mute all of the participants in the meeting.
Select Manage Participants in the toolbar.
Click the Mute All button at the bottom of the Participants window. This will affect the host who clicks the button, and it will also affect any other co-hosts and attendees.
A dialog box will open with a checkbox to Allow participants to unmute themselves. After checking or unchecking that box, click Continue to mute all current and future participants. Note: Even if you uncheck Allow participants to unmute themselves, the host and co-hosts will always be able to unmute participants.