#1 download audacity https://www.audacityteam.org/

#2 at the top go to file> import> audio. Then find your music file of choice.

#3 at the top go to tracks> mix> mix stereo down to mono

#4 at the top again go to file> exportAudio> select OGG in the format tab> click export

#5 name the audio file and match the name in the xml, example below

    <turnOnVehicle turnOffIfNotAllowed="true" >
        <sounds>
            <work file="sounds/NateTribute.ogg" volume="6.2">
                <volume indoor="8" outdoor="7" />
            </work>
        </sounds>
		<turnedOnAnimation name="shakingAnimation" speedScale="1" />
    </turnOnVehicle>