For once, I agree with hornfixer!
Do a thorough search of the forum and you will find much, much information about becoming a tech, including books to buy, tools, and plenty of advice.
Sadly, there is no such thing as "certified" when talking about repair techs. I have personally had experiences with graduates of repair school who were very, very bad at repair and also ones who were very good at repair. I have also seen a lot of very, very good technicians who never went to repair school. I have seen great techs that are not members of NAPBIRT, and I have seen bad techs that are- and I have seen the inverse of both situations as well! I think you get my drift- There are many paths to becoming a repair tech.
I personally never went to repair school, am not a member of NAPBIRT (although I keep meaning to join), and I am head woodwind technician at a large store in New York City and I have plenty of work to keep me busy.
FWIW, I was a music ed. major in college, although I didn't finish. Being able to play the many instruments I learned in my pedagogy classes has certainly helped me during my repair career.