The part fan is the fan you see on the front of the print head. First thing I’d check is the connection from the fan to the print head board is good. Also, make sure something wasn’t sucked into it preventing it from spinning, you should be able to spin it easily by hand.
The Aux fan is the large fan located on the side of the printer, it provide additional cooling for your parts. Do a google search for “P1S Part Fan” and there’s a couple of videos showing you the different fans.