Install gkrellm-volume by entering the following commands in the terminal:
sudo apt update sudo apt install gkrellm-volume
Description:
A mixer plugin for GKrellM
This GKrellM plugin allows you to control the mixer of your soundcard.
Homepage: http://gkrellm.luon.net/volume.php
Version: 2.1.13-1.1build1
Section: universe/sound