If you have a Windows 10 tablet (such as a Surface) and you're looking to only use one specific camera for either webcam photos or QR Code usage you can do so a few different ways.
If you're using Chrome to access Buddy Punch the browser will allow you to specify which camera is used, so that the main camera isn't disabled for all apps.
If you aren't using Chrome you'll want to disable the camera you don't want to use & enable the one you do. Check Device Manager> System Devices. You should see both Microsoft Cameras listed there. (it's important to note that the Microsoft Cameras are NOT listed under 'Imaging devices', but rather under 'System Devices')