A professional iPhone repair service can be found in most major cities and many of the smaller sized ones. You can do an online search to find an iPhone repair that is near to you.
You do have to take that into an iPhone Repair store. Or as an option you could mail it to them but it makes more sense actually to take it in yourself. You may have to do without it for at least 24 hours. You just need to choose a repair shop that does repair work to iPhones. Some places specialize in them whereas others can fix most models of cellular phones including the iPhone. If you have an iPhone 6 you may have to discover one who has a great deal of experience in this generation iPhone. When you take it in they will ask what is wrong with it and if you know then inform them. However, they will still hook it up in their store to check it out for all its functions.
There are great deals of things that can go wrong with an iPhone that you may need to search for an iPhone repair service store close by. You may have an LCD screen that begins to bleed colors into each other or one that the liquid crystals begin to get green or another color for a weird screen impact. Typically you can still use your iPhone until you can get that screen replaced unless you have dropped your iPhone and the screen cracked or broke. However, if your mobile phone struck the ground hard enough to break the screen, then you may have to get your entire iPhone repaired or replaced.
There are other things that can break on the iPhone. For example, the battery may die. It has a rechargeable battery. However, that does not mean that the battery will always recharge. It might wear out or have other problems with it. The battery is not meant to be changed by the owner, but it is created to be taken to a service center or in the manufacturers viewpoint taken to the Apple iPhone shop for a replacement battery. If at the Apple iPhone store they may talk you into getting a brand-new iPhone.