Hi,
If it's anything like the 'connects2' canbus adaptors then that missing connector is for the steering wheel remote. These are available from most car audio shops.
Just guessing, based on my 'connects2' adaptor. From the Quadlock plug connected to the car loom going to the adaptor, the red & white twisted pair look like the canbus input, the yellow permanent live, black ground. From the adaptor to the Dynavin unit ISO plug, the red will possibly be switched live controlled by the adaptor. You may have other wires for lights, reverse, handbrake, and canbus.
Please don't take this as fact, it's only an educated guess as I'm not familiar with Dynavin wiring. So please check with a multi-meter first after unplugging the Dynavin. Twisted pair wires will usually be for the canbus network signal, do not fiddle with these.