For the second stimulus payment, there isn't anything for you to do, because it will come automatically. But if you don't get one or both payments,you can claim the Recovery Rebate Credit when you file your 2020 taxes and it will provide the same amount of payment as the stimulus would have. TurboTax will guide you through this when you prepare your return.
This is what the IRS says: "The IRS is working hard to deliver the second Economic Impact Payment quickly, as required by law, while still preparing for the upcoming 2021 tax filing season. Due to the compressed timeline, the IRS is unable to reissue and mail checks and instead encourages people to file their 2020 tax return electronically to claim and receive the Recovery Rebate Credit quickly as possible."
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