In the handle of clicking on a marker, you need to create a cycle for all markers and find the one whose coordinates coincide with the coordinates of the selected marker.
This means using a lot of code block. Thats too bad. Actually this is fatal situation for my app. Is there an example block? (Who is admin? Please someone tag him/her.)
I think you will be interested to see this project. On the Canvas tab, create several polygons, turn on Select, click on the marker and on the free space of the field.