These videos may help you gain a better understanding of how to interface external pedals with Helix.

Video specifically about H9: https://youtu.be/_dQLbpA83xE

Here’s another example that talks about using the CC map on an external device (REVV D20) to program snapshots. You can just consult the CC map on H9 Control by going into the Pedal tab, MIDI Settings, Assign MIDI CC Messages, and there you will see what CC#s have been assigned to control the H9 functions. All of that is customizable.