Pull up and down until it loosens. Release the cloth under neath the zipper, and then pull until it becomes loose. If the zipper teeth are damaged or missing, the entire zippe
…r must be replaced. If the zipper just keeps popping open, you probably just need to replace the slide or "pull" Look on the back side of the slide and there will be a number and/or letter. Number denotes size (5, 7 or 10 is most common for coats or jackets) and the letter usually tells what style (plastic, metal, coil etc.) Cobbler shops usually have replacement slides for most zippers and they can usually replace it while you wait. Costs run $5 to $10 installed, (versus $40 to $80 for an entire new zipper!) If you can buy just the slide from a shop, it's very easy to install 90% of jacket zipper slides. At the top of the zipper will be "stops" or little tiny U-shaped pieces of metal crimped on above the top tooth of the zipper. They're there to prevent you from pulling the slide all the way off, hence "stops". Carefully remove it by opening it slightly using a pair of dikes or side cuts...wirecutters to the layman. Just use the sharp edge to get in between and squeeze lightly. The stop should open just a bit. Carefully remove it and put it somewhere nearby, DONT LOOSE IT! You only need to take off the stop that's on the same side as the pull (slide). Now pull the original slide all the way off the top, you might have to twist it a little, but it should come right off. Now take the new slide and work it back on, from the top down, on the same zipper track you just took the old one off. Grab the tab of the slide and twist back and forth until it drops freely onto the zipper teeth and falls to the bottom. Now take the "stop" and crimp it back on and your done. If you got the right slide it will zip right up tight just like a new jacket. As a former cobbler myself that did a lot of jacket repairs, I would say 7 out of 10 bad zippers were just the slides. They wear out much quicker than the teeth and then cannot mesh both sides together fully. Support your local cobbler!! You'd be amazed at what they can create and repair. And in this economy "Repair and Save!" (MORE) 
