Select an IED in the System Diagram right click and use the option "IED Data Model"
STS shows a tree based representation of the data model of this IED.
The Tabs at the bottom of the main window give access to the data over different point of view.
You can edit all IEC 61850 information in this editor. However this should be only done by experts. The changes may not be recognized by the manufacturers IED Tool or th etool will fail to load the resulting SCD file.