1. You're going to need a bachelor's degree (or higher) in, specifically, music therapy from an American Music Therapy Association (AMTA)-approved program. At this time, there are more than 70 colleges and universities that provide this as an undergraduate degree.
2. A six month internship is currently required too, and lucky for you, there are internships offered all over the country in a variety of places so that you can get an idea of the type of setting you're interested in.
3. You also need to get certified from the Certification Board for Music Therapists.
4. You'll need to study for #3.
5. Proficiency in guitar, piano and/or voice.
Just like getting a regular Bachelor of Arts (or even Bachelor of Fine Arts), you’ll get lots of music classes, sure, but you'll also take courses in psychology, biology, and social and behavioral sciences. And, like every freshman going through the motions of trying to get through that first year, you may even find yourself in a class called "Historical Sewing Techniques for Practical use."
Look at the colleges that offer this degree, poke around to see if you or any of your friends, friends of friends, or friends of your enemies (who are your friends, according to...well, war rules) know about any of these schools. Visit the schools. Ask a lot of questions. Get a feel for dorm life and what lies beyond that sewing class....