When a decedent, or a person who dies, leaves a will, a proceeding must be completed in the Surrogate's Court to probate or prove the will. After completing the forms, file all documents with a deputy clerk in the Civil Department, along with the filing fee.Requirements: The will, if the decedent had one. A certified copy of the death certificate. Use Form RP524, Complaint on Real Property Assessment to grieve your assessment. Call 516-908-8842 Or Fill Out the Form Below. How to fill out the Nassau County Property Tax Grievance Form Instructions? 1. Read the eligibility criteria carefully. 2. Tangible personal property. Tax notices are mailed to the owner's address as it appears on the certified tax roll, normally on or before November 1st.