Purse zippers are easy to fix. Remove the clip at the start of the zipper and slide the zip back on. Then replace the clip. This will require long nose pliers or similar tools.
When I have followed the above directions, I run a candle down the zipper and up again. This makes the zipper slide more smoothly for several weeks or much longer. If the cloth of the zipper has begun to fray, you can often use a safety pin or two to hold it together. Then brush white glue on the fabric but not the metal parts. The white glue will stiffen the fabric and make it last longer. Jewell
If the zipper can't be fixed and you can't replace it yourself, take it to either a tailor or a shoe repair shop....most can replace it for you.
If the problem is that the zipper teeth separate after being zipped closed, the repair is simple. Open the zipper all the way and gently press together the front and back face of each side of the zipper pull with a pair of broad nose pliers. Rub teeth with a bar of soap and zip closed. (Zipper pulls are made of notoriously soft metal and can develop a gap with normal use.)