What is the form to fill out if Someone filed your taxes without your knowledge?

If someone filed your taxes without your knowledge, you should fill out Form 14039, the Identity Theft Affidavit. This form notifies the IRS that you are a victim of identity theft and helps protect your tax account. Additionally, you may need to provide supporting documentation and possibly file a police report depending on the situation. It’s also advisable to monitor your financial accounts and consider placing a fraud alert on your credit report.