I retract my previous statement. I had some free time so I looked deeper into your question.
The short answer is: DockingUtilities.findTabbedDockableContainer(Dockable).setSelectedDockable(Dockable);
The Dockable parameter in DockingUtilities.findTabbedDockableContainer() will give you the TabbedDockableContainer that it belongs to.
Then the Dockable parameter in TabbedDockableContainer.setSelectedDockable() will set focus to that Dockable making it the visible tab.
Sorry it took so long to get you an answer, I have been busy with my day job and a personal project.
I attached an example if anyone needs it.