@kostaman
Thank you for your responce.
I saw that thread, but it said to try amixer sset ‘Audio hdmi-out mute’ on.
The output I got was:
CoreELEC (official): 9.2.5 (Amlogic.arm)
CoreElecBed:~ # amixer sset ‘Audio hdmi-out mute’ on
amixer: Unable to find simple control ‘Audio hdmi-out mute’,0