If you got the recovery rebate credit on a 2021 tax return it will be on line 30 of your Form 1040.
But some people did not have to get it as a credit. Many people received it before they filed their 2021 tax return as an automatic direct deposit from the IRS, so you also need to check your online account with the IRS to see if you received it.
https://www.irs.gov/payments/your-online-account