How to update field Service Type from a Workplan Template task?

Summary:

We are using Workplan template to add automatically tasks to an existing project

The business requirement related to Service Type values for some of the tasks from Workplan template has been changed and we need to update the Service Type field for Workplan Template related tasks.

The issue is that the Service Type field is not exposed on the Manage Workplan Templates application screen and neither on the REST API

Please advise How to update field Service Type from a Workplan Template task?

Thank you,

Costin