If someone you do not know filed a tax return with your Social Security number included on the return and it was accepted by the IRS then you will have to print and mail your tax return. You do not amend a tax return that has not been filed.
If you did not receive the 3rd stimulus payment then you should have indicated that when completing your return. The Recovery Rebate Credit will be entered on your federal tax return Form 1040 Line 30
Verify that your IRS tax account does not show you receiving the 3rd stimulus payment. Go to this IRS website for your tax account - https://www.irs.gov/payments/your-online-account
If you checked your bank account in the March - May 2021 timeframe and there is not a $1,400 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...
See this TurboTax support FAQ for printing and mailing a tax return using the online editions - https://ttlc.intuit.com/turbotax-support/en-us/help-article/printers-printing/print-mail-return-turb...
You also should report the identity theft to the IRS. Go to this IRS website for identity theft - https://www.irs.gov/newsroom/taxpayer-guide-to-identity-theft
