You should first calibrate your expression pedal from the system settings. This must be done using the H90 pedal UI: https://cdn.eventideaudio.com/manuals/h90/1.3.0/content/system-menu/io.html

In H90 Control, you can set the range for any parameter by adjusting the highlighted circle around the parameter. For example, load Program 2 “Bedroom Vibes” and you’ll see that the Speed parameter is mapped to HotKnob A, but the range is limited from 4-7.5 Hz.

Let me know if you have any other questions.