there are 4 ways:
1. your car has TV module or you install TV module (~$200-$400). then power camera from relay and connect it to TV module. there is a backup camera pin on tv module to switch video input.
2. you install video switch module from BMW (designed for backup camera functionality without TV tuner)
3. you install not-OEM video module that is connected to OEM navigation ~$200 on eBay
4. you install not-OEM head/navigation (like Hooligan) with built in rear camera input.