When you go to the DSHS website, you will se a link for the necessary forms. Be sure to give them an itemization showing when he stopped paying. In addition, if it has been a very long time, you can take the matter into the court here and have the arrears reduced to a judgment and have 12% simple interest added to all delinquent payments and they will also then collect the back interest. That can be substantial. See the court faciliator for help with paperwork.