For some reason, there was no easy way to turn the volume up/down. The little mixer button in the notifications are of the panel had disappeared. So I went to Applications->Settings Manager->Panel. Then I chose the Items tab, clicked on the ‘+‘ button and chose the Indicator Plugin from the list of optional extras.
I then used the Up (or down) arrow on the Right-hand side of this tab to position the indicator where I wanted it, made no other changes to the settings, and clicked Close.
Oh yes! One little Volume Control button now back where it should be! 🙂