You control the Highfive conference room device using either your laptop or iPhone/iPad.
Computer: If you started the conference using your laptop, click on the Mute Mic button in the menu bar of the Highfive Application. This will stop the device from sending conference room audio to remote participants. Clicking the button again (now called Unmute Mic) will re-enable the microphone.
Mobile: If you started the conference on your iPhone/iPad, bring the Highfive app to the front, click on the video to show the UI elements, and click on the Mute button.