Failure to do so may result in the dismissal of your petition. Support Modification Packet Forms and Instructions, pdf document.1. Fill out a child support modification petition. 2. File the petition with the Family Court that most recently established your order. This document is a sample form letter designed for individuals seeking a downward modification of their child support obligations. Child Support Forms. No information is available for this page. Fill Out The Petition For Modification Of An Order Of Support - Nassau County, New York Online And Print It Out For Free. First, you need to file a written petition with the Court which includes your current address. Contact the initial agency that issued the original child support agreement.