Are you looking into why this incredibly powerful DSP box can't even do a simple volume control or wah-wah effect? I am so close to selling it, there is very little that it does that other pedals don't do as good or better.
If you want to calibrate your expression pedal for your H9, you can use H9 Control to do that. You need go to Pedal Settings -> General Settings -> Pedal Calibration Disabled, and click from Yes to No, then move your pedal from heel to toe for a couple of times. You can check if it's perfectly calibrated in the Presets screen, see if the heel and toe move the ribbon from the left end to the right end. After it's calibrated, please go back to the Pedal Calibration Disabled page to lock the expression by clicking Yes.
If you need to use your expression pedal as a wah-wah pedal, you can use the Q-Wah algorithm. Factory preset F6 Vintage Wah is a good example. If you set TYPE parameter to WAHWAH and SHAPE parameter to EXP PDL, you can use your expression to do wah-wah effects.