RB Perimeter Dotted Lines Deleting

I am playing RB and I thought I’d try the perimeter dotted lines to mark the end scenario perimeter. Now I find that after being placed I can’t select and delete them after saving(no back button). I’m not using the arrow method perimeter lines. Any help would be nice. Thanks.

I just found that shift-Left click will select the lines and then R click to delete, also works with overlays.