Generally, for a credit or refund, you must file Form 1040X within. You can now file Form 1040X electronically with tax filing software to amend your Form 1040, 1040SR, or 1040NR for the current or two prior tax periods.Please contact us if you have additional questions. You can find the CP or LTR number on the right corner of the letter. File an amended return if there's a change in your filing status, income, deductions, credits, or tax liability. RITA will prepare your return for you. Fill out this sheet, attach your documents and drop it off at select RITA locations. Read the letter carefully. Most IRS letters and notices are about federal tax returns or tax accounts. If you have additional inquiries, you may submit them on the Questions, Comments, or Requests form.