iPhone 12Pro Max

You will see an Unknown Part  message if the camera installation is incomplete or if the camera:

• Was replaced with a nongenuine camera
• Was already used or installed in another iPhone
• Isn't functioning as expected

This message doesn't affect your ability to use your iPhone or access your camera.

This excerpt was taken from: About genuine iPhone cameras - Apple Support

AFAIK, Apple does not provide a user method to remove this message. As such, I suggest that you contact Apple Support directly for further assistance with this matter. To do so, simply select the "Support" link on the lower left-hand side of this forum's web page.

By getting your phone serviced by Apple or an authorized repair center.

Something has gone wrong with your camera.