File a 2020 and/or 2021 tax return to claim any missed stimulus payments.
The IRS is no longer sending out stimulus payments. Missing amounts will be included as a part of your tax refund as a Recovery Rebate Credit.
File 2020 to claim the first two payments and 2021 for the third payment. If you already filed those years, file an amended return. The IRS corrected returns that had the wrong stimulus amounts, but the service did not add stimulus payments if you did not claim them on your 2020 and 2021 tax returns.
You can only prepare the current tax year online in TurboTax. To file prior year returns, buy the prior year programs and install them on your computer.