How to change Active Marker Icon?
The active marker is used when you click on a marker, the active marker image is used instead of the default marker, to modify the active marker, update the marker with marker name as "Active", as in the screenshot below.
Image of Manage Marker, Active Marker
To modify the image, update the the image of active marker, in case if you don't have this marker, you can create a new marker with marker name as "active".