Select a slider that matches the one you are removing. The letters that are printed on the slide tell you what size you need. With a seam ripper, carefully remove stitching around lower ends of zipper tapes. Pry off metal stop at bottom of the zipper, careful not to tear the tapes at the base of the zipper teeth
Remove old zipper foot. Take new zipper slider and guide track tapes into the top grooves of the slider, pushing them through to the bottom. Use a pin if needed to work the track tapes through. Pull tapes gently to make sure slider is sitting evenly on tracks. With both tapes threaded through slider, gently pull slider up until locked track teeth appear at bottom.
Sew a new stop at bottom of the tracks with needle and thread. Sew zipper back onto garment where stitching was removed for repair.