If you are within 24 hours of the 747 departing, then it is under airport control and I doubt anyone can do much about it until you get to the departing airport. If it is more than 24 hours you could ring up and see if they can help. Normally you do get the option to select seats but I have had one situation where it didn't, however that was straight after a hanging screen on the first attempt. However - given that it's not upper deck, it's not a bad seat for a night flight. Away from the galleys and you'll be nicely cocooned in there. So I wouldn't try too hard, there are worse seats.