Complex sentence: The era name was changed to mark the start of a new cycle of the Chinese zodiac in "Genna" 9, the 30th day of the 2nd month.
Split into simpler sentences: The era name was changed to mark the start of a new cycle of the Chinese zodiac. The previous era ended and a new one commenced in "Genna" 9, on the 30th day of the 2nd month.