Money in a dependent care FSA can sometimes be rolled over, but only if your plan allows it (not all do) and only to be used in the first 2 months of the new year.
Your money is simply forfeit. When you run the dependent care interview in turbotax, it will pick up the total amount of the benefit from your W-2 box 10. Then it will ask you for the name of the qualifying person you paid for care for, the name of the provider, the amount spent on qualified care, and any amount forfeited in the account. You won't be taxed on the amount forfeit but you don't get it back, either.