You do not have to amend your tax return. The $1,400 payment is your third stimulus payment. It does not affect your 2020 tax return. The third payment will be reconciled on your 2021 tax return that you file next year.
There is no reason to amend because you received the $1400 3rd stimulus check. There was no place at all to put anything about that check on a 2020 tax return. You could, however, enter whether you received the 1st or 2nd stimulus amounts by completing the recovery rebate credit on your 2020 return. Did you receive the 1st check for $1200 or the 2nd check for $600? If not then you can still get those by entering it on a 2020 return or an amended 2020 return.
The IRS will not calculate the Recovery Rebate Credit for people but if you make a mistake on the Line 30 amount, the IRS will calculate the correct amount of the Recovery Rebate Credit, make the correction to your tax return and continue processing your return. If a correction is needed, there may be a slight delay in processing your return and the IRS will send you a notice explaining any change made.
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How do I amend my return showing my recovery rebate credit as 0 how do I remove my recovery rebate credit
You do not amend your tax return to correct or remove the Recovery Rebate Credit. If you claimed a Recovery Rebate Credit that you are not entitled to, the IRS will make the correction.