Did you click that big orange button that said “Transmit my return now?” If you did that, you cannot do anything to fix it yet. You have to wait for the email that tells you if your return was accepted or rejected.
You cannot change or add anything on the return that you just e-filed, nor can you stop it. It is too late, just like when you put an envelope in a US mailbox on the corner. The IRS does not allow you to take it back.
If you left out a W-2, a 1099G, or a dependent, or a 1099 etc…DO NOT change your return while it is “pending.” The changes will go nowhere.
Now you have to wait until the IRS either rejects or accepts your return. If your return is rejected, you will be able to go into your account and make the necessary changes to your tax return and re-submit your return.
If the IRS accepts your return, however, then you have to wait longer until it has been fully processed and you have received your refund. THEN you can prepare an amended tax return and e-file or mail it in. You have to be able to work from that return exactly the way it was when it was e-filed originally. You will need to use a form called a 1040X.
Meanwhile, DO NOT go in and start changing anything on your return in the system, or you will make a mess for yourself. Sit tight and wait until you see what the IRS does with the return you just e-filed
Here is how to amend your return (How to File an Amended Tax Return with the IRS) "If you prepared your original tax return using TurboTax, log in to your account, open the tax return you already filed, and click on the link to amend your return. From there, the software will walk you through the process of filing the amendment."
As @xmasbaby0 mentioned, you will need to wait until the IRS accepts your return to make an amendment. If it happens to be rejected, you can simply make the updates to remove the child along with fixing what caused the rejection, and e-file again.
And....if in fact you need to amend....the 1040X you need will not be available until mid-February, so you have to wait for several weeks.
You should also know that if there is another parent who can claim the child for 2024, their return will be rejected if you filed first and the IRS accepts your return. If that happens, they have to file by mail. They will not be able to file a return claiming the child by e-filing it this year, even if you amend.