There can be two options in case of a coat zipper repair. The first is when the zipper slider has to be replaced. It is a lucky situation if nem the whole zipper has to be replaced since the zipper "chain" is not damaged but only the slider is broken, hence a fairly quick would be sufficient. 

The other zipper repair option in case not the zipper is damaged but in fact the seam between the tape and the cloth. With these coats we need to strengthen the sewing hence there is no need for zipper replacement. In case you have a more severe problem than you will need a zipper replacement  instead.