Each MIDI CC message you send to the H9 tells the parameter you set it to control to go to a certain value.  For example, if you set parameter 1 to respond to CC05, and then send a 0 to CC05 (on the MIDI channel you've set for the H9, or any channel if OMNI), parameter 1 will be set to its lowest value.

This gets a little tricky in some cases, because we have to map the parameters, with whatever range they may have (for example, Dry/Wet mix parameters go from 0% to 100%), where MIDI CC values go from 0 to 127.  To get around that, we re-map the parameter values to set MIDI CC values; for example, to get 100% wet, you would send a 127 to that MIDI CC event number, and other Dry/Wet values will map into the range between.

Other parameters have different ranges and possible, so it might take some exploration to find exactly the behavior you want for any given parameter.