Deductions & credits

When I enter the previous $1800 that I received from Letter 6419 the refund monitor then removes the other half of $1800 that I am to receive. I have fully completed my taxes but I am trying to figure why im not receiving the other portion that was suppose to be on the refund. It does talk about the Schedule 8812 on the letter however TurboTax has no information how to fill the form to attach to the Taxes.