As the graphical configuration editor show a lot a pins, it is not obvious to see where is it present inside the textual editor.
For showing the textual pin configuration of a configured pin from the graphical editor, you must use the 'Show pin in Xtext editor' context menu.
This will open the textual editor if not already opened, and will place the cursor location near the concerned pin configuration.
Now that the pin is located inside the textual editor, you can modify the register field instances of this configuration, or change its name, using the textual editor like described in the chapter named manipulation of a pinmap configuration.
A similar operation is done whenever you move the edition cursor inside the textual editor, if the graphical editor is opened as well (as in the picture above). The selected pin will be shown and centered in the graphical editor.