My daughter has a masters in special ed with a concentration in music. She hated classroom teaching (special ed but the principal used her as a sub for general ed all the time) and left the field but she is thinking about pursuing another masters’ in music therapy because she prefers working one on one or in small group settings and loves music. She checked out some online programs just by googling music therapy graduate programs. There was one in Colorado where you only had to go out there for about a week to do clinical and the rest was online. Some of her credits would have been usable. NYU also has a program but it was wildly expensive and I’m sure it was worth it.
If you are just starting out, look up music therapy undergrad programs and see what you find. You will probably have to take some psych classes. My D took psych 101 but would need to take developmental as part of a masters. She also took sped courses in working with different types of populations and some of those might transfer, depending on the program she chooses.
You also need to consider what population you want to work with. Do you want to work with children, the elderly or everyone else? There are schools, special ed schools, hospitals, nursing homes, etc. that all offer music therapy programs. My d prefers the elementary aged and younger people but one of her friends like working with the elderly because she loves music from the 40’s and 50’s.
Good luck.