If you are wanting two external buttons to work the spindle speed up/down then easiest way would be to set them up as OEM triggers in ports and pins, Inputs. Next you would go to Config menu then system Hotkeys and enter the oem codes next to the oem triggers you are using.
For the spindle speed up the oem is 163 and down is 164
If it is something else yo are wanting try again as I am just not quite clear what you are asking.
Hood