Can anyone advise please what is wrong and how to fix it please?
OBD is showing ambient air temperature sensor circuit high
The ambient air temperature sensor is the one that reads the temperature outside the car, it's used by the air conditioning system. It's safe to drive your car with this problem, although your AC may not work properly.
As for getting it fixed, the sensor has failed, or the wiring to the sensor has developed a problem. The sensor is usually somewhere in front of the radiator. This answer for the 2010 Insignia says the sensor is behind the lower front left bumper, I don't know if it's the same for the 2017.