Working with Ardour-built Plugin Editors
To view a plugin editor, double-click on the plugin within the processor box. A new window will appear showing the editor/GUI for the plugin.
Add a pic showing the generic GUI
If a plugin does not have its own GUI, Ardour will construct a generic plugin editor from a small set of common control elements. Ardour will do this even for plugins that have their own, if Edit > Preferences > GUI > Use Plugins' own interface instead of Ardour's is disabled.
The generic UI can be temporarily switched to by context-clicking on a processor and selecting Edit with generic controls. This is necessary in order to access the plugin automation controls.
In the generic UI, any controller can be reset to its default state by Left-clicking on it.