We are trying to update SharePoint Library Document Set property from Component Workflow and in order to do that we are using Update List Item action. But that is giving error "Unable to find list item to update".
If you are running the workflow from the document library, you should be able to use the update list item and connect to the correct field property that you are wanting to update.
Can you share a screenshot of what you are seeing?
Also what are you really wanting to do that is causing you to update the document set from a workflow?