Change Marker from external click

HTML

<script src="http://maps.google.com/maps/api/js?sensor=false&amp;.js"></script>
<div id="results"></div>
<div id="map"></div>
<a id="markerSwap" href="">Click Me to change color</a>

CSS

#map {
    width: 450px;
    height: 400px;
}

JavaScript

// This example adds three custom symbols to a polyline.

      function initMap() {
        var map = new google.maps.Map(document.getElementById('map'), {
          zoom: 6,
          center: {lat: 20.291, lng: 153.027},
          mapTypeId: 'terrain'
        });

      // Define the custom symbols. All symbols are defined via SVG path notation.
      // They have varying stroke color, fill color, stroke weight,
      // opacity and rotation properties.
        var symbolOne = {
          path: 'M -2,0 0,-2 2,0 0,2 z',
          strokeColor: '#F00',
          fillColor: '#F00',
          fillOpacity: 1
        };

        var symbolTwo = {
          path: 'M -1,0 A 1,1 0 0 0 -3,0 1,1 0 0 0 -1,0M 1,0 A 1,1 0 0 0 3,0 1,1 0 0 0 1,0M -3,3 Q 0,5 3,3',
          strokeColor: '#00F',
          rotation: 45
        };

        var symbolThree = {
          path: 'M -2,-2 2,2 M 2,-2 -2,2',
          strokeColor: '#292',
          strokeWeight: 4
        };

        // Create the polyline and add the symbols via the 'icons' property.
        var line = new google.maps.Polyline({
          path: [{lat: 22.291, lng: 153.027}, {lat: 18.291, lng: 153.027}],
          icons: [
            {
              icon: symbolOne,
              offset: '0%'
            }, {
              icon: symbolTwo,
              offset: '50%'
            }, {
              icon: symbolThree,
              offset: '100%'
            }
          ],
          map: map
        });
      }