First of all, you don't want to try to fix it yourself. Go back to the dentist who placed it. If it is just a superficial chip, it can often be smoothed down and not really apparent to others. If it's a big chip, it is pretty difficult to try to add a patch of plastic composite bonding onto the porcelain veneer to fix it, and thus may have to be completely remade.
If you need to have one or more veneers replaced because of chipping, make sure that the dentist evaluates, and if necessary, adjusts your bite. Also, your dentist may suspect that you are a night time grinder (bruxer) or clencher, and recommend that you wear a night time appliance to protect your teeth and veneers. That is called a "night guard appliance."
Also, if you are needing the veneer to be completely replaced, ask your dentist what kind of porcelain he used? The weakest is feldspathic porcelain (the original porcelain used when porcelain veneers were first introduced to dentistry in 1985). A stronger porcelain material that has been used for the past 15 years is Empress pressed ceramic. However, the latest state of the art porcelain material is EMax porcelain. It is extremely strong, and for those who want only mimimal drilling on their teeth that need veneering, EMax can be made much thinner and needs much less drilling. EMax has been my favorite porcelain veneering material for the past two years.