From what I can tell that MIDI footswitch sends out program change messages on the left and right switches and MIDI CC messages on the center switch. Isn't it already increasing and decreasing the presets?

In H9 Control if you click the Pedal button in the bottom menubar and go to MIDI Settings, you'll see a button labelled "Assign MIDI CC messages to pedal functions" and another labelled "Program change receive map".  That's where you can set up what particular kinds of MIDI messages do on the H9.  You'll most likely want to go to Assign MIDI CC messages to pedal functions / Toggle between Active and Bypass for the active/bypass function.