If the touch tone is enabled on the LG unit, the volume can also be adjusted in the tone settings.

Android 9 | LG UX 9.0
System Sound Volume -  Open the  Settings
System Sound Volume -  Tap on  Sound
System Sound Volume -  Tap on  Volume
System Sound Volume -  Move the  Slider  to adjust the  system volume
  1. Open the Settings
  2. Tap on Sound
  3. Tap on Volume
  4. Move the Slider to adjust the system volume

LG Instructions
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