To start with your needs and possibilities. For self-dismantling your phone, you will need to collect a lot of information. In principle you can do this by registering at the special portals and forums for artists repair. There you will find a lot of useful information and will be able to ask questions to professionals. And if you're lucky, and get good answers.
Now you have to buy a special tool for disassembly of the apparatus. And then you have to take the risk and try without special diagnostic equipment to determine the fault. Often this repair is to replace damaged parts. For example, a damaged phone screen. This way you can learn to do simple repairs.
In order to become a true master on repair of cell phones, be prepared to spend the time and incur the cost of training. The easiest way in this case - the admission to study in specialized educational institution which trains such specialists. But, unfortunately, not very much. Usually this course at any big service center. Find out if there is any centre in your city and contact there. In fact, very few of them, so the most common path of the other.
In the absence of your city, special training courses find the largest and well equipped service center or repair shop. The idea of the level of professionalism of the masters in your enterprise you can create, examine reviews of urban forums. Find out if there are vacant seats for masters or students. In most cases you will be offered an apprenticeship with the prospect to hold the position of master after passing the training course.