To request a tax refund, file an Application for Refund - Sales and Use Tax (Form DR-26S) or Application for Refund - All Other Taxes (Form DR-26). Once the Cost Containment Unit (CCU) has reviewed the overpayment, you will receive a letter explaining the details of the reconciliation.Report an overpayment. Complete an overpayment refund form to notify First Coast of an overpayment prior to receiving a demand letter. When you identify a Medicare overpayment, use the Overpayment Refund Formto submit the voluntary refund. Please download the form, complete each field and print. Include the form with your refund so we can properly apply the refund and record the receipt. All applications for refund must contain: • A detailed explanation of how the refund amount was computed;. • The specific reason(s) for the refund request;. Use Form 843 to claim a refund or request an abatement of certain taxes, interest, penalties, fees, and additions to tax.