I don't understand your question.
You have to open the public transport information window, open the window for the transport you desire ( e.g. bus), search through your whole lines until you can open the window in the screenshot.
I would like to "click on the line directly on the street" ( like when you add or remove a bus stop ), e. g. the blue bus line, and open this little window.
Another way to do it is by clicking on a bus en route and then clicking Modify Line, but that's not any more direct.
Thanks! That is not totally direct, but way better. It is way faster to find a bus on the route instead of the line in the gui.