The second Economic Impact Payment was $600 ($1,200 if married filing jointly for 2020) plus $600 for each qualifying child you had in 2020.
The second Economic Impact Payment was reconciled on the 2020 Federal 1040 tax return. The 2020 Federal 1040 tax return would need to be amended to receive the second Economic Impact Payment as a Recovery Rebate Credit.
See IRS FAQ here under Recovery Rebate Credit Topics view Topic G Correcting Issues after the 2020 tax return is filed.
IRS FAQ A8 here states:
If a trace is initiated and the IRS determines that the check wasn’t cashed, the IRS will credit your account for that payment, but the IRS cannot reissue your payment. Instead, you will need to claim the 2020 Recovery Rebate Credit on your 2020 tax return if eligible.
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