Even the session is live, you can change your camera or microphone. Or if the Camera or Mic is not working, then you can change it too. Go to Settings->media->change devices. There you can click on audio input and video input to select the microphone and camera you want.
You can check that device by clicking on Check device, if you are able to see and hear yourself then you are good to go. Now your video and audio are going through the external camera and microphone respectively. See the below images for more info.