Add Firebase extension to Xamarin.Forms project to show image inside the push notifications

I'm using FirebasePushNotification Plugin for Xamarain to receive push notification and I have it working fine. However, I would also like to display custom images on each push notification (apart from the App logo which is already displayed fine) when the App is backgrounded. I have read that it is required to add a Firebase extension to do this but haven't found sample code to do it. All I would need is the code needed to make the example project [login to view URL] be able to display this extra image on the push notifications managed by the OS when the App is in the background. I should work both on Android and IOS