You should not have to reboot, you just need to calibrate and map the controller.

Just to confirm, you’ve calibrate the footswitch and when you depress it, Sw4 turns on and off on the H90 UI?

If that works, can you try mapping a parameter, selecting “Learn” for the control source, and pressing the footswitch?

https://cdn.eventideaudio.com/manuals/h90/1.5.2/content/edit-modes/parameters.html#mapping