Buy yourself a MVV (Munich Public Transportation) ticket at one of the many vending machines at the airport. For round-trip tickets please choose the Single-Tageskarte (Gesamtnetz) for 10,80 €.
Take the S8 from the airport towards Herrsching and exit at the 5th station, Unterföhring (see map below).
Go towards the retail stores (displayed). You arrive at a courtyard with a large bronze sculpture.
Turn to the left upon exiting the station and walk down Bahnhofstraße.
While walking on the left side of the street, you will reach the office after about a 1 minute walk.
Phone: (+49) 89 4613570-0
Fax: (+49) 89 4613570-90
For more information, visit the public transport website: http://www.mvv-muenchen.de/en/home/index.html