I used the schematic, Owen pointed you to a source.
That schematic is actually from here, I think: https://github.com/olliw42/storm32bgc/tree/master/storm32-bgc/storm32-bgc-v130-eagle-gerber-files-20140322
Olli W’s Wiki and GitHub are the reference for all things Storm32.
My method was to use the schematic as a starting point, and then check everything with my multimeter (in “beep” mode) to ensure the connections were actually as in the schematic. Unfortunately there were a few pins that were different (reversed order on the header, things like that) on my AliExpress ordered Storm32 compared to the schematic, so it is worth checking the pins you plan to use.