That part of the program may not be updated yet. You should not file until after January 15, because that's how long the IRS has to pay the second stimulus payment. And in any case, the IRS won't open e-filing until January 27 or later. Any returns e-filed before then will only go into cold storage.
You need to list your child as a dependent. Make sure the birthday is correct and that you enter the child's social security number. If the child does not have an SSN, you will not get the child tax credit or the stimulus, so don't file until the child gets their SSN. Select that the child lived with you all year, which is the correct answer for a newborn.
Then, finish the interview in order and you will get to the section for stimulus payments. Enter the amount you actually received from round 1 and round 2. If you qualify for more (due to your new dependent) the amount will be added to your tax refund.
