How can I change and marker/pin icon on custom map using XamarinFormsMaps?

In addition, Android 9 has removed the Apache HTTP client library from the bootclasspath, and so it isn't available to applications that target API 28 or higher. The following line must be added to the application node of your AndroidManifest.xml file to continue using the Apache HTTP client in applications that target API 28 or higher:

<application ...>
   ...
   <uses-library android:name="org.apache.http.legacy" android:required="false" />    
</application>

The following snippet is an example of the settings that must be added to AndroidManifest.XML:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionName="4.5" package="com.xamarin.docs.android.mapsandlocationdemo2" android:versionCode="6">
    <uses-sdk android:minSdkVersion="23" android:targetSdkVersion="28" />

    <!-- Google Maps for Android v2 requires OpenGL ES v2 -->
    <uses-feature android:glEsVersion="0x00020000" android:required="true" />

    <!-- Necessary for apps that target Android 9.0 or higher -->
    <uses-library android:name="org.apache.http.legacy" android:required="false" />

    <!-- Permission to receive remote notifications from Google Play Services -->
    <!-- Notice here that we have the package name of our application as a prefix on the permissions. -->
    <uses-permission android:name="<PACKAGE NAME>.permission.MAPS_RECEIVE" />
    <permission android:name="<PACKAGE NAME>.permission.MAPS_RECEIVE" android:protectionLevel="signature" />

    <!-- These are optional, but recommended. They will allow Maps to use the My Location provider. -->
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <application android:label="@string/app_name">
        <!-- Put your Google Maps V2 API Key here. -->
        <meta-data android:name="com.google.android.maps.v2.API_KEY" android:value="YOUR_API_KEY" />
        <meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" />
        <!-- Necessary for apps that target Android 9.0 or higher -->
        <uses-library android:name="org.apache.http.legacy" android:required="false" />
    </application>
</manifest>

Declaratively - The MapFragment can be added via the XML layout file for the Activity. The following XML snippet shows an example of how to use the fragment element:

<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@+id/map"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          class="com.google.android.gms.maps.MapFragment" />

Programmatically - The MapFragment can be programmatically instantiated using the MapFragment.NewInstance method and then added to an Activity. This snippet shows the simplest way to instantiate a MapFragment object and add to an Activity:

var mapFrag = MapFragment.NewInstance();
    activity.FragmentManager.BeginTransaction()
                            .Add(Resource.Id.map_container, mapFrag, "map_fragment")
                            .Commit();

This interface has a single method, IMapReadyCallback.OnMapReady(MapFragment map) that will be invoked when it is possible for the app to interact with the GoogleMap object. The following code snippet shows how an Android Activity can initialize a MapFragment and implement the IOnMapReadyCallback interface:

public class MapWithMarkersActivity : AppCompatActivity, IOnMapReadyCallback
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        SetContentView(Resource.Layout.MapLayout);

        var mapFragment = (MapFragment) FragmentManager.FindFragmentById(Resource.Id.map);
        mapFragment.GetMapAsync(this);

        // remainder of code omitted
    }

    public void OnMapReady(GoogleMap map)
    {
        // Do something with the map, i.e. add markers, move to a specific location, etc.
    }
}

My question is in the map implementation

CustomPin pin = new CustomPin
        {
            Type = PinType.Place,
            Label = "Test pin",
            Position = new Position(37.79752, -122.40183)
        };
        map.CustomPins = new List<CustomPin> { pin };
        map.Pins.Add(pin);