Since you are using the BSEC Arduino library, there is a funtion to do just that: setTemperatureOffset(float tempOffset). This means that you could add iaqSensor.setTemperatureOffset(4.6); in your setup() function to subtract a fixed 4.6°C from all temperature compensated outputs.
If you dig a little into the source code, you will see that whatever value fed into setTemperatureOffset() will be used to set BSEC_INPUT_HEATSOURCE 😉 Therefore yes, this is the correct way to input your external temperature influence so that all BSEC outputs will be compensated for it.