If you were being claimed as a dependent on a 2020 or 2021 tax return you are not eligible for a stimulus payment.
If you were not a dependent then you have to file a 2020 and 2021 tax return to claim the Recovery Rebate Credit for the stimulus payments that you did not receive. The Recovery Rebate Credit is entered on Line 30 of the Form 1040. The stimulus amount is $1,800 on the 2020 tax return and $1,400 on the 2021 tax return.
IRS Form 1040 for tax year 2020 - https://www.irs.gov/pub/irs-prior/f1040--2020.pdf
IRS Form 1040 for tax year 2021 - https://www.irs.gov/pub/irs-prior/f1040--2021.pdf
A 2020 and 2021 tax return can only be printed and mailed, it cannot be e-filed.
Print, sign, date and mail the tax return to the IRS. Include with the mailed return any forms W-2 and 1099 which have taxes withheld. Go to this IRS website for mailing addresses - https://www.irs.gov/filing/where-to-file-paper-tax-returns-with-or-without-a-payment
There are no penalties for filing a tax return after the due date if filing for a tax refund or there are no taxes owed.
