My divorce decree did not cover our agreed upon split of my 401K. The amount is not in dispute, how do I get a QDRO in WA?

The usual procedures would involve getting a court order regarding the division of the money in the 401k and sending a certified copy of the court order to the 401k administrator in your company. The administrator would then review the court order to make sure it has the provisions required by law and by the company. If the court order is acceptable, the administrator fills out the necessary documents to have the trustee of the 401k divide the 401k funds according to the court order. Many bigger trustees may have preprinted sample QDRO forms or applications that can generate the forms based on input from a plan participant. Fidelity seems to have such an application. Have you asked the plan administrator whether the company has sample forms? "We used an arbitrator and represented ourselves pro se." There's your problem. The only documents the court generate on its own in a dissolution case are bills and notices when the parties do not comply with court rules and orders to dismiss the case when the parties do not come into compliance. The court is not going to write up the QDRO for the parties. Because retirement plans are authorized by federal laws, the federal government requires that QDROs contain certain provisions. To protect themselves from later being sued by one or more of the parties or others, the employers and trustees also likely would require certain provisions in the documents and certain procedures to be followed. While there is no law that requires real persons to hire attorneys to represent them, the courts expect persons who represent themselves to follow the same procedures and laws required of attorneys. "Can I do this myself?" The procedures are not difficult to follow. The contents of the documents are not mysteries revealed only to the initiated. So, yes, I suppose you can do it yourself especially if you two are in agreement. In fact, you may have to do it yourself as most attorneys are risk averse and likely would not want to touch the case at this point. You can contact the "arbitrator" and check whether the person can draft the document for you or can recommend someone to draft the document for you. (I suspect that you did not use an arbitrator as that term is used legally since arbitrators are generally involved when the parties do not agree with each other.) You can also contact a few law offices and check whether they would draft the documents for you.