...
To control WebRTC calls using a headset you must first activate headset controls and then connect your headset.
Activate headset controls
To activate headset controls, enable the setting in WebRTC Options. Go to Settings in ContactPad and click WebRTC options. The available options appear in a new browser tab. Within Advanced in WebRTC options, select to enable Activate headset controls (beta)a compatible headset.
Connect WebRTC to your headset
To connect to the headset, you must have a WebRTC tab open. For information about opening a WebRTC tab, see the Popping out the active ContactPad section in Identifying which webpage contains the active ContactPad. On the WebRTC tab, click Connect headset. (If Connect headset is not available, you must activate headset controls. For information about activating headset controls, see Activate headset controls earlier in this page.) In In the dialog box that appears, select the compatible headset you want to use to control WebRTC calls and click Connect. Refresh the WebRTC tab to activate the connection.
...