Make sure all rear camera cables are firmly plugged in. One connector is near the rear of your car, about 50 cm from the rear camera.
Unplug the rear camera cable from the front iQ dashcam, then press the reset button on the top of the front dashcam and plug the rear cable back in.
Open the iQ app, go to iQ Settings, and tap Add rear camera (fifth option on the settings page).
Follow the on-screen steps to reconnect your rear camera.
Once connected, your rear camera will start showing new files and live view in the app.
If the rear camera still does not display, check that your iQ is on the latest firmware via the iQ Support page or firmware update option in the app.