Someone else may be able to answer this better than I can, but all I can say is that when you get on the ship, go to the dining room and ask to be changed to the second seating for dinner. However, this may be a wait list basis, as the second seating may be completely filled, which is probably why you were assigned the first seating for dinner.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)