First, see if the IRS ever issued you the stimulus payment in 2021. Go to this IRS website and sign onto your tax account - https://www.irs.gov/payments/online-account-for-individuals
If the EIP3 payment of $1,400 was not issued by the IRS then you will need to amend your 2021 tax return and complete the Recovery Rebate Credit section of the federal tax return. The 2021 tax return has to be printed and mailed to the IRS on or before April 15, 2025 to receive the credit.
See this TurboTax support FAQ for amending a prior year tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
