https://developers.arcgis.com/net/api-reference/api/netwin/Esri.ArcGISRuntime/Esri.ArcGISRuntime.Mapping.FeatureForms.FieldFormElement.UpdateValue.html
Method UpdateValue
Use ArcGIS Maps SDK for .NET to build powerful desktop and mobile apps that incorporate capabilities such as mapping, geocoding, routing, and geoprocessing.
method