Take it out during the daytime and don’t transfer any data over yet and have a backup phone ready. When in bright light the iPhone will use the telephoto lens and cover the other two lenses with your finger so you can test to see if the telephoto camera works. Another trick you can use is to shine a light into the lens and you should see a sensor since the sensor is offset by a prism and no longer directly behind the lens. If the camera doesn’t work take it to Apple to have the phone replaced.