If you have already filed your return then you will need to see if your return gets accepted or rejected.
- If your return has been rejected by the IRS, then all you have to do is add your 1099-R for the 401k withdrawal on your return and refile.
- If your return has been accepted by the IRS, then you have to file an amended return (1040X) to make changes. But please wait until your refund or payment is processed. Please be aware that you can e-file your 2021 amended federal tax return, but most states require amendments to be printed and filed by mail. Please see How to amend a tax return for instructions (this will update once 2021 Form 1040-X is available).