You have evidently gotten far enough to have removed it, and I will assume you know how everything correctly lie's within the cavity. Making sure the pushrod coming rearward off the trigger is lined up to enter the recess in the front of the rebound spring housing, insert the spring in the housing, then slide the housing (forward side down) into position until you are fully in place and (of course can't push it over the stud), using a medium to larger Phillips screwdriver with one of the grooves in line with the stud, push the point in the back of the spring coil and push forward and down until the edge of the coil of the spring slides over the stud. Then take a flat screwdriver blade and and push in and down on the top of the coil and it should push into position. There are a number of special tools made for this operation, and if you are going to do more than this one I would recommend you acquire one. I also recommend you look up on youtube a video of a S&W assembly or dis-assembly and watch it a couple times. Once you do it a time or two It isn't difficult, but the special tools make it much easier.
