If the Tasks feature layer is published as REST service on a standalone ArcGIS Enterprise feature, stop the Tasks feature service on the Enterprise Server Manger. Update the domain and contingent values using ArcGIS Pro. For more information, see Updating Domains and Updating Contingent Values sections in the Configuring and Deploying the Task Feature Layer chapter.

Start the REST service on the Enterprise Server after the update. The forms should reflect the new value.