Close external window from source application

I am trying to close the external browser window from the source application (wda). But it seems that I am unable to close from the source window, just by calling close method. This close method has a parameter '  control_to_focus_id' . I am not sure what exactly it needs to be filled with.

But anyways these act like two separate sessions and can't communicate any longer.

Is there a way for me to control the external window and close on some user action at source/

Any inputs would be highly appreciated.

Thanks