How can i change the volume value in tribblix?

I recently installed Tribblix but can't find any mixer program like freebsd's mixer(8) on the system

Kanninha what happens when you type "mixerctl -a" ?

Kanninha Explained here. You'll have to install, at a minimum, these overlays:

root# zap install-overlay all-audio-drivers legacy-audio

There's also the multimedia overlay. (See list.)

In addition to what @rvp said, see the man page for audioctl http://www.tribblix.org/man/man1/audioctl.html