Setting the camera and microphone used by the publisher

You can have the publisher use the rear-facing camera of the device by setting a properties prop of the OTPublisher component and setting the cameraPosition property of that object to "back":

<OTPublisher
  properties={{
    cameraPosition: 'back',
  }}
/>

Note that you can also publish a screen-sharing stream — one in which the source is the client's screen, not a camera. For details, see Screen sharing.