The nearest airport to Heilbronn is the Stuttgart Airport (STR), 50 km away.
For international attendees, Stuttgart (STR) and Frankfurt (FRA) are recommended. From there, you can take a train. You can search for connections on the Deutsche Bahn webpage. As destination, enter "Heilbronn Theater". As source enter either "Stuttgart Flughafen/Messe" (for STR) or "Frankfurt(M)Flughafen" (for FRA).
Information for local transportation by bus, train, tram, and for arriving with a car, parking possibilities etc. are available on the Bildungscampus homepage.