The bottom RIght of the screen is a menu called Audio.
It will have two numbers like: Audio(2,1) (yours will be different);
The first number is green is the number of audio channels available
The second number is red, is the number of audio changes muted.
Audio(2,1) => Two audio channels availablve, one muted.
Click on the Audio(2,1) and a menu pops up:
Click on the Dot to the left to enable/disable that channel