Wyo. Stat. Ann. § 41-7-407

In case of omission to assess any person or land that should be assessed for benefits, or additional assessment, or to award damages, said omitted party and the owners or person entitled to the possession of omitted land may, in writing, agree with the commissioners of said district that the assessment should be against said land, or against said person, or what said damage should be, and such agreement shall be acknowledged and witnessed as provided above for waivers, and be filed in the court.