You just have to activate the plugin and go building your posts, pages or projects; you will find in the Divi Audio module some new design options both under the ‘Content’ tab (‘Audio Timeline Margin’ setting under ‘Audio’ toggle and ‘Image Width’ under ‘Image’ toggle) and in the ‘Design’ one (here you will find at the top a new ‘Audio’ toggle to customize timeline colors and other).
More info on www.howidivit.com/i-divi-advanced-audio/
This plugin is available for download for your site.