You can find the CP or LTR number on the right corner of the letter. Use Form 843 to claim a refund or request an abatement of certain taxes, interest, penalties, fees, and additions to tax.Review and process individual state tax returns for Suffolk City residents. Each return is reviewed for completeness and accuracy. How do I Request IRS Verification of Nonfiling Letter? Check the box below that indicates your reason for filing Form 843. Tax. Abatement or refund of tax other than income, estate, or gift tax. Step 1: Complete the taxpayer information section. Dear Suffolk County Resident: Welcome to the Office of the Suffolk County Comptroller. We are here to serve you in any way possible.