If the IRS sent you the 3rd stimulus payment it will be shown in your IRS online account - https://www.irs.gov/payments/your-online-account
If you are Married Filing Jointly also check your spouse's tax account.
If you checked your bank account in the March - May 2021 timeframe and there is not a EIP3 payment from the IRS then go to this IRS website for how to start a trace on the payment - https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...
