1. Press the SETUP key and choose your setup
2. Press the EDIT key
3. Press your left MORE soft button until you see VTRIGG
(which stands for velocity trigger)
hit that soft button and it will bring you to 4 options
Vtrigger 1
Vtrigger 2
Vtrigger 3
Vtrigger 4

assign them to taste and exit -
it will ask you do you want to save... say yes.