Armitron Men's 204379BKSV Silver-Tone Stainless-Steel Bracelet and Black Dial Dress Watch, we replaced the battery and can't get the back on the watch.

Usually you would need a watchmakers press for closing the watch back. Without proper tools it is quite difficult, but you can try the following. Take a leather belt and lay it flush on an even, solid surface (stable table will do). Undo the strap (both ends) from watch case by pushing spring bars inwards with pen knife. Lay the watch crystal face down on the leather belt. Belt must be wider than watch itself and the leather must be quite hard and even, not soft. Find the small groove on watch case back and align it very carefully to the watch's winding stem, so, the stem goes directly in the middle in protrusion. Slightly push the case back into the watch case at that groove point and gradually apply pressure with fingers going all way around the case back. Use your body weight if needed. You should hear "click" sound when the case back jumps in to place. If this does not work, there is no other way, but to go and see watchmaker. Hope it will work for you.