The Assign Drawing(s) Label Workflow can be created from CAD Documents of type Drawing:

Once the Change Item profile card appears, fill in its Description and choose the Drawing Label you need to apply:

You can change the Label of multiple Drawings with the same Change Item. 

To do that, you simply need to add the Drawings by accessing the "Root Objects" tab from Workflow profile card, and selecting the highlighted icon: 

You can then launch the Workflow by using the following icon from its Profile Card header:

Complete documentation: Assign Drawing(s) Label Workflow FAQ