Familiarize yourself with adding actions to buttons. 

The command to mute / unmute one or more audio sources is mute

The parameters are;

• val=<0, 1 or * >
• delay=<time in millisecs> (optional)
• <audio source>
• <audio source> (optional)
• <audio source> (optional)

The val parameter can be 0 (unmute), 1 (mute) or * (toggle current setting).

The optional delay specifies a time (in milliseconds) to wait before running the command.

Example - toggle the current mute state of the Aquarium and Music audio sources