Where to file your taxes for Form 1120-S ; A foreign country or U.S. possession. You can get in-person help at your local IRS Taxpayer Assistance Center.Call for an appointment after you find a Taxpayer Assistance Center near you. How Do I Register My Business? Corporations file Schedule M-3 (Form 1120) to answer questions about their financial statements and reconcile financial statement net income (loss) To schedule an appointment, call 844-545-5640.