Customizing data pulled into Google Maps info window via the KML feed

I'd like to customize the data that is pulled from the KML feed. Currently all data is pulling, I really just need the date, time, lat, long, and maybe the speed and heading. Here is my current script

var map;
      var src = 'https://share.garmin.com/Feed/Share/sailforepilepsy?d1=2020-07-11T02:19Z&d2=2020-07-12T23:59Z';
      function initMap() {
        map = new google.maps.Map(document.getElementById('map'), {
          center: new google.maps.LatLng(-19.257753, 146.823688),
          zoom: 6,
          mapTypeId: 'terrain'
        });

        var kmlLayer = new google.maps.KmlLayer(src, {
          suppressInfoWindows: false,
          preserveViewport: false,
          map: map
        });
        
		var infowindow = new google.maps.InfoWindow({
    	content: event.featureData.infoWindowHtml
  	});
	
  marker.addListener("click", function() {
    infowindow.open(map, marker);
  });
      }

I'm assuming I just need to somehow define specific content elements to pull in? I can see a list of the items, but not how they are defined.

Thanks!
Lauren