To enable or disable Audio (mute video) please go to Players page
On the Player page, you will have a list of players in your account.
To enable or disable mute click Edit icon on the right of the player.
In the Muted, section selects On or Off.
Videos that have Autoplay On must be muted in order to play them on all modern browsers.
After you finished editing it make sure to Preview player behavior to make sure you got the desired outcome.