If you are asking about becoming an automotive technician I recommend contacting vocational programs in your area. If you are asking about automotive engineering then you would be best served by getting a bachelors degree in automotive engineering from an ABET accredited university.
Depends on what aspect of automotive you're interested in! For example, I work in research for an automotive company - I have a degree in advertising, but no automotive-specific experience. For a more hands-on role such as a service technician, there are various certifications you can receive through vocational programs, community colleges, etc.