He means the minus button on the remote control
I had the same problem and solved it like this

I've had this problem too,
but there's no need to panic.

Just re-pair the subwoofer with the console.

Place the subwoofer with power supply next to the console.

2. everything must be switched off

e. Press and hold the subwoofer minus for at least 3 seconds in switched off mode.

4. enjoy the sound

have fun