Mailing addresses for Forms 941 ; Department of the Treasury Internal Revenue Service Kansas City, MO 64999-0005. Internal Revenue Service PO Box 806532Overpayment as a nonemployee, file Form 941 for each delinquent quarter. Should be similar with a state form as well. As a business owner (SCorp) I pay monthly tax deposits towards quarterly tax return, form 941. I accidentally overpaid deposit for May 2017. To start, download Form 941-X from the Internal Revenue Service website. Line 15 - Overpayment: If line 13g is more than line 12, enter the difference on line 15. DO NOT fill out both lines 14 and 15. Bystep explanation on how to fill out Form 941.