For 2020? You already filed 2020? Without it?
DO NOT CHANGE ANYTHING YET! WAIT. If you did change it then put it Back.
You cannot change or add anything on the return that you just e-filed. It is too late, just like when you put an envelope in a US mailbox.
Now you have to wait until the IRS either rejects or accepts your return after Jan 27 when the irs starts processing returns. If your return is Rejected you can go back into your account and fix it, then resubmit it.
But if the IRS Accepts your return you have to wait even longer for the IRS to fully process your return and you get the first Refund. You will still have to pay the tax due if you owe on it. THEN you can prepare an amended tax return and mail it in.
How to amend
Did you do this to e-file the 2020 tax return -
You complete your tax return by finishing all 3 Steps in the File section. In Step 3, to e-file your tax return, you must click on the large Orange button labeled "Transmit my returns now".
After completing the File section and e-filing your tax return you will receive two emails from TurboTax. The first email when your tax return was transmitted and the second email when the tax return has either been accepted or rejected.
If you did now you have to wait. The IRS will not be accepting or rejecting any 2020 federal tax return until late January 2021.
If the tax return is rejected you can add the W-2 to your tax return and re-submit.
If the tax return is accepted then you have to wait to receive the federal tax refund. Then you have to amend the 2020 tax return by using Form 1040X. The amended tax return has to be printed, signed, dated and mailed by you to the IRS.
The IRS will take 4 months or longer to process the amended tax return. So if your the amended tax return has a tax refund, you will not receive the tax refund until June or July 2021, maybe even later.