Volume locked on sound strip in VSE In VSE I have a sound strip where I adjusted the volume and then accidentally clicked the dot icon to the right of the volume box which seems to have locked the volume and changed the dot to a diamond so I can't alter it now. See image.

How can I undo that?  I've tried clicking it again, and selecting various menu options but no luck so far!  (Blender v2.82a)
You have added a keyframe. It can be deleted by clicking on the diamond again, or right-clicking in the number widget and select "Clear Keyframes":