Summarize the following:
Even if the zipper is structurally sound, sometimes some coaxing is needed. Gently unzipping the zipper further and then trying to zip it back up will sometimes solve the issue, especially if the zipper just caught on something. This step is common, so you may have already tried it. If you haven't, try pinching the fabric below the zipper to squeeze the garment into its zipped position. Do this while gently coaxing the slider of the zipper upwards. This step can help if the issue is caused by the teeth trying to pull away from each other. Another common tactic that you can try is pinching above the zipper. This tactic helps gather teeth together when they're having a hard time catching, and it can help in cases where the zipper is having trouble because your tailored slim-fit trousers or flirty cocktail dress are a little too tight. If the zipper is still sluggish, closely examine the zipper. Make sure there isn't anything like thread or hair stuck in it. If something is in the way, pull it out to see if that fixes the problem, as it can keep your zipper from closing easily. You may need to move the zipper back and forth as you try to pull the thread or hair out of the zipper. One of the most common problem areas for a zipper is actually the teeth. Over time, the teeth can get bent out of alignment. Look to see if all of your zipper's teeth are straight and in line. If they're not, you can use pliers to pull them back into place. Just don't be too rough, as you can pull the teeth off. Another option is to just replace the zipper completely. You can do it yourself at home, or you can take it to a tailor's to be replaced. Most sewing stores sell zippers you can use to replace the one you have. However, having a professional do it will be easier, and it doesn't cost too much.
Coax the zipper. Pinch below the zipper. Pinch above the zipper. Look for anything in the way. Check the teeth. Replace the zipper.