My wife's Iphone 6S has what appears to be a dust smudge on the camera sensor. It's not on the external lens but inside so I suspect based on Google searches, it's probably a speck of dust on the sensor which magnifies to a light smudge about 3-4mm in diameter.

Is there anything we can do to fix this? The phone is about 2 years old but it wasn't bought in NZ so the CGA probably won't apply. I read that the sensor has to be replaced which seems like major surgery.

Thanks for any tips else I will be buying a new phone :-(