I noticed an error in my taxes immediately after filling. What can I do?

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

If you need to change your return that was already e-filed, you would need to amend it after the IRS had processed it as @xmasbaby0 stated.

There are times when you should amend your return and times when you shouldn't. Here are some common situations that call for an amendment:

• You realized you missed out on claiming a tax deduction or credit.
• You accidentally claimed the wrong tax filing status.
• You need to add or remove a dependent.
• You forgot to claim taxable income on your tax return.
• You realize you claimed an expense, deduction, or credit that you weren't eligible to claim.

See this article and this one for more information on filing an amended return with TurboTax.

@troyhudetz