iPhone 7 plus overheating

The rear camera of my 7 plus shut down and I changed a new phone 20 days ago. Thought it would be fine this time. Today it suddenly started to get hot under the camera and then spread all over the back of the phone. Removed the case, closed all the apps, turned off the screen and it cooled down quickly. Then I turned on the screen, didn't use any app, and it started to get hot as ****, especially the camera area. Really worried my camera will burn down again. Too bad it has passed return date and now I have to stay with the phone that has problem after problem since I bought it. Anyone knows how to solve it? Do I need to restore?