To claim a refund, you must file an amended return within 3 years after the date you filed your original return or 2 years after the date you paid the tax. The additional time, provided in Notice 202321, to file an amended return is automatic.Receive an IRS 4364C letter? Complete your amended return as if you are filing the return for the first time. Submit all the forms relevant to the information in your amended return. You must file Form 1040X within 3 years after the date you filed your original return or within 2 years after the date you paid the tax, whichever is later. Download Form 1040-X from the IRS website. Thank you for your amended return. We have adjusted your account as you requested.