Updating on ArcGIS Online
If the Tasks feature layer is published as a hosted layer on ArcGIS Online, then the feature web layer has to be overwritten on ArcGIS Online. 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.
Publish the Tasks feature layer, overwriting the original web layer with the new updated values.
Note: The form on the Tasks feature layer must be saved on the Map and not on the layer. This will prevent the form to be overwritten when the Tasks web layer is published to be overwritten.