Do you have a RED speaker with a cross line like mute on the right top corner if yes press F8 if not
play something a channel and you will see a speaker when you move your mouse click on that and adjust the top two lines
if you have reduced the volume with the remote and you back out of KODI before turning it to max, you will need to turn the volume up until you turn the volume up and exit KODI. The volume is kept at the level you leave KODI when entering again.
