Unfortunately, you may be too late. Guests can make reservations for Disney dining 180 days out from the start of their reservation. You are a little over a month out. Is free dining going on during your stay? That will decrease any chances of getting anywhere to eat.
The only way to make reservations is to call Disney Dining. Or you can wait until you get there, but that reduces your chances even more.
If you are going September 26th of this year, I would recommend calling now (if not yesterday )...and every time you get a chance between now and your trip.
They are likely already booked, but you may get lucky and catch a cancellation.
Cinderella's Royal Table must be paid for with a credit card at the time of booking and must be cancelled at least 48 hours (or is it 24?) in advance or there will be no refund. Because of this policy, most cancellations will probably happen just a day or two before hand.
If you can't get in, just keep trying right up until the end of your trip. You just might get lucky!