You cannot delete presets..once there is something there.. you can't get tha 'Insert Preset Here" slot again.
Easy workaround? Make an empty preset- like a reverb with everything set to Zero. Lable it "BLANK". And copy that into every slot you want to be 'empty'.
Then.. set your range to only include whatever 68 or how many presets you want.
How so? When II send the list to the pedal from the computer, it's filled with empty slots. When it imports them from the pedal, to the iPhone, it's filling them up?
Please try to change your H9's preset range to 1-99, and see if there are any more presets beyond preset 68. My guess is the presets are always there. When you transfer your preset list from computer to H9, it replaces the presets within the preset range of that preset list. However, the rest presets on H9 remain on it but you never go there.