Sorry for the issues you are having. It’s best to start simple with no MIDI splitter etc. A few things you can try:
Do you have another MIDI device that can send PC messages to the H90? Connect the device directly to the H90 via MIDI and it should change Programs on the H90 with no further configuration.
Does the controller work to send PC messages to another device using the same settings that aren’t working with the H90?
What messages exactly are you sending from the MIDI controller? Are they PC messages with a corresponding number (ie. PC1, PC2, etc.) or are you trying to increment/decrement/load Programs on the H90?