WordPress expert required to write wp_localize_script for WP Audio default plugin

General information for the website: Music website
Kind of development: Customization of existing website
Description of requirements/features: Hi I am looking for someone to provide a piece of code for my website (which has now been launched). I have edited the core files for now but I am looking for a workaround.

I am trying to add a function in my WordPress Child Theme file functions.php. I need it to make the audio player start volume .3 instead of the default .8

I have found the file in wp-includes > js > mediaelement > mediaelement-and-player.min.js with 2 instances of the StartVolume value in. Obviously I don't want to edit the core files.

I have found this code to edit this in functions.php but it doesn't seem to work (maybe as it is from an old thread):

wp_localize_script( 'wp-mediaelement', '_wpmejsSettings', array( 'pluginPath' => includes_url( 'js/mediaelement/', 'relative' ), 'startVolume' => 0.3 ) );

Can anyone tell me what it should be? My WordPress installation is in a subfolder but I understand this is not a problem when the 'includes_url' is used.

This is the website (player on home page) - as mentioned at the moment I am controlling the volume by editing WordPress core :(

http://www.andrewgregory.net/