The solution to the problem that the zipper on the side of trousers can't be pulled up is to smear crayons back and forth on the two rows of zipper teeth, which will be slippery next time, or you can use candles. When metal zipper is used for a long time, the zipper will loosen, the caliber will become larger, and it is difficult to pull it up.
If the pull ring on the slider falls off, you can install a paper clip instead of the original zipper. If you don't have a paper clip, you can prepare a key ring, put it on the pull ring, and then buckle the key ring on the trousers button so that it won't slide down again.