The stimulus payments that are being sent out currently are based on the 2021 tax return. These payments are going out to people that didn't claim the credit on their 2021 tax return.
If you filed your 2021 tax return and didn't claim the Rebate Recovery Credit, the IRS will automatically be sending out payments.
If you didn't file your 2021 tax return, you will need to file the return to claim the credit.