Miniamp 1.0, pin38, gpio20 (PCM)

Hi, can someone explain what pin 38 do an where it goes to on the print? I found schematic that shows that pin 38 is not used, but description from HiFiBerry tells it is used for audio. don’t ask why but I removed the 40pins bracket from my HiFiBerry miniamp 1.0 and destroyed some of the connections on the print. I figured almost everything out except pin 38. Link of schematic https://forum-raspberrypi.de/attachment/19897-miniamp-schematic-pdf/