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.
If you left out a W-2, 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 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. You cannot e-file an amended return. They have to be mailed, and it takes about 4 months for the IRS to process an amended return.
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
Since you have filed your tax return and then discover that you have an additional W-2 to file you will have to wait until the IRS either accepts or rejects your tax return.
If the return is rejected you will correct the error that caused the rejection, add the W-2 and refile your return.
If the return was accepted by the IRS then you will have to file an amended tax return using Form 1040X to add the W-2 to your tax return
This link to the TurboTax Help page How to amend (change or correct) a return you already filed provides information on how to amend your tax return.
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