If you did not claim the child as a dependent on the 2023 tax return you filed then you will have to amend the 2023 tax return to add the child as a dependent.
In the My Info section of the program when entering a dependent you need to indicate that the child lived with you for the Whole Year if the child was born in 2023.
If the return is accepted you will have to amend your original tax return. An amended return, Form 1040-X, can only be printed and mailed to the IRS if the original tax return was not e-filed. The IRS will take up to 20 weeks or longer to process an amended tax return.
Before starting to amend the tax return, wait for the tax refund to be received or the taxes due to be paid and processed by the IRS.
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...