Enabling Mono Audio from the Accessibility shortcut
You can quickly enable Mono Audio from the Accessibility shortcut in the System menu. For more information on enabling and using the Accessibility Shortcut, see our article How to enable the shortcut to accessibility features in Chrome OS
Note: If this does not work it could be because someone else manages your computer settings (an IT department or administrator). If this is the case, you will need to contact them to access these settings or for further help.