You cannot amend a return that was never accepted by the IRS, so if your 2019 tax return was never accepted for whatever reason, you will need to file the original return to take care of your filing obligation for 2019.
To get your 3rd. stimulus check, however, you can simply file a tax return for 2020.
When you prepare your tax return for 2020 in TurboTax, you will be prompted to enter how much you received for your stimulus and then the program will calculate the amount of stimulus due you based on your income, number of dependents and payments already received. If any additional stimulus is due you, it will be used to reduce your 2020 income tax liability, and the balance will be refunded to you.
You will see the options when you are done entering your tax information and proceed to the review process.
You can file a tax return in 2020 to get your stimulus check, even if you aren't required to otherwise.
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