As the publisher of an editable feature service, you can set default z-values for layers in the feature service. This default value will be applied any time an editor inserts or updates a feature through the feature service but does not specify a z-value.
For example, if you edit a feature service in ArcMap, z-values can be set using the Sketch Properties tool 
on the Editor toolbar. If you edit a feature service in ArcGIS Pro, you set z-values in the Modify Features pane.
Caution:
If you set a default z-value for a feature service, when editors update features in the feature service using a client that does not support specifying a z-value, the existing z-value will be replaced with the default.
Configure default z-values when publishing
When you publish a feature service from ArcMap, you have the option to configure the feature service to insert default z-values when the client does not provide values. This is set on the Feature Access tab of the Service Editor. See Editor permissions for feature services for more information on setting feature service properties when publishing.
Configure default z-values on an existing feature service
The following steps describe how to configure a default z-value for an existing editable feature service:
- Open ArcGIS Server Manager and log in as the owner of the feature service or as the ArcGIS Server administrator.
If you need help with this step, see Log in to Manager.
- Click Services > Manage Services.
- In the Services module, click the name of the feature service for which you want to set default z-values. If you don't see your service in the list, it may be located within a folder in the Site (root) directory.
- In the Edit module, click Capabilities.
- Click the Feature Access option (the name, not the check box) under the Select and configure capabilities window. This displays the feature service properties.
- Check the Apply default to features with z-values check box.
- Enter a default z-value. This value will be applied to all inserted and edited features in z-enabled layers in the feature service if the client or editor does not specify a z-value for the feature.
As noted above, if the feature service is edited in a client that does not allow the editor to specify a z-value for a feature, the existing z-value will be replaced with this default value when the editor updates a feature.
- Click Save and Restart to apply the changes to the service.