Simplify the following text for a Grade 8 native English-speaking person.
Original: From September 1907 through October 1908 Kellner fulfilled his initial military reserve duty in the 6th Infantry Company of the Leibregiments GroÃ herzogin ( 3 .
Simplified: In 1907 and 1908 Kellner had to fulfill his military reserve duty . He was assigned to the 6th Infantry Company of the Leibregiments GroÃ herzogin ( 3 .