Hi,
I take it your spindle is on the Zaxis, try this script with your 'go to work zero' button.
local inst = mc.mcGetInstance()
local executeGcode = ("G00 G53 Z0.0000\n") --use machine coords (G53)
mc.mcCntlMdiExecute(inst, executeGcode)
mc.mcCntlSetLastError(inst, "Moving Zaxis to zero using Machine Coords")
Good Luck!