Try to become an apprentice at a local shop. Else, buy some junkers and go through some trial and error. There's various books and videos. If you have good mechanical intuition, then learning how to repair saxophones will be a very fulfilling journey. There is some up front investment in tools, and I recommend leaving the really troublesome things like dent removal to your local shop, but there's no reason you can't learn how to clean, repad, do springs, adjust action, etc. on your own. Beware. The first time I disassembled and reassembled my horn it took me about 10 hours and I was in a panic by the time I was done. Now I can do it and have everything clean and back together in about 2 - not including a repad or a spring job. Being curious gets you halfway there. Just proceed with caution and patience and ask questions.