Fill out the correct form for your business. To quickly search for a notice or letter on this page, you can press Ctrl-F in most browsers and type in the number or name, then press Enter.If a letter is about a changed or corrected tax return, the taxpayer should review the information and compare it with the original return. Send a typewritten letter to the IRS office that sent the notice. Use the format in the sample letter below. Sending an IRS audit reconsideration request? You can find the CP or LTR number on the right corner of the letter. If you made a mistake in entering a social security number, a payer's identification number, omitted a form, or misspelled a name, you can correct these errors. You generally have 30 days to respond to an IRS notice, so there's no reason to ignore it. Always check which tax year the notice relates to.