If you have multiple camera or microphone sources connected to the device you are using to go live, you can switch between these different cams and mics.

To change which camera and microphone are being used during your live session:

• Click AV next to SETTINGS
• Select your Video, Audio, or Speaker source 
• Click APPLY

If you don't see the device you wish to use, make sure to disconnect and reconnect it as you should see it become an option.

You can also flip the preview view the flip icon here: