2 things;
PETG should need NO Cooling fan. Only time it is needed is if you are printing something tall and very thin.
If you place a hot end you need to run a PID on it so it will maintain the proper temp. This calibrates how the main board controls the power to the heater.
I can not tell you how to do it on your machine. Google your model and "Performing a PID calibrations "
Good luck