How can I loop through screen areas and point to specific area? To loop through screen areas and find IMAGE_EDITOR I do:
for area in bpy.context.screen.areas:
    if area.type == 'IMAGE_EDITOR':
        # Do stuff

But what if I have three image editors opened and for example I want to point the second one?
Not sure what do you mean the second one but you can select the second one with further conditional list:
[area for area in bpy.context.screen.areas if area.type == 'IMAGE_EDITOR'][1]

And also there are properties x and y for area type, which indicate the bottom-left corner position in your screen. You can write some sorting function to select the desired one.
Area(bpy_struct) — Blender Python API