Your iPhone 7 camera flashlight isn't working, you can try this:
Use Control Center to test the LED flash. Turn the flashlight off and on. If the LED flash doesn't work as a flashlight, contact Apple Support.
If the flash isn’t working, or it goes off every time you take a photo, check your flash settings. Tap in the upper left of the screen to choose a different setting.
If you take extended video with the flash on, or you’re using the device in a very warm environment, you might see a message that says the flash is disabled. The message remains until your device cools down.
If this still can't help, maybe your camera is broken, we have similar repair video about iPhone 6,
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