Did you already file? Yes you can amend to add your baby. You need to wait for it to be fully processed and you get the first refund. Then you can Amend.
When you add them under My Info. You need to answer 2 questions…..
Did your child live with you for the whole year? Answer YES even if they were born late in the year even on Dec 31. And same for how many months in the USA
Then was at least half of child's expenses paid by CHILD? Usually is NO, Child didn't pay for more than half of their living expenses.
Here's the problem...to claim the $2000 child tax credit, you must file an "on time" return containing the child's social security number. On time means the return was filled before April 15, or will be filed before October 15, but only if you asked for the automatic extension. You should have asked for an extension and waited for the SSN. Because you did not wait, adding the child on an amended return will give you a $500 credit for "other dependent" but you will not be eligible for the $2000 child tax credit or EIC. Turbotax may show you an additional refund of $2000 or more on your amended return, but you should expect that the IRS will reduce it before they actually pay it.