presuming its for the s14 in your sig then
pull the handbrake cover off, look on shaft of hand brake lever there will be 2 metal tabs about 2'' from the top, get a screw driver (flat head) and pull the tabs out to release the spring, put the cover back on and slide the knob over the original button, job done
if its a toyota or mazda, unscrew original button, remove spring, screw drift button on, job done.