I would expect it under "Backcar setup" menu in settings, but I found only "Line type" and "Line position" options, which does not turn off the lines completely. E.g. Teyes has not only such a possibility, but also much detailed setup of lines:
Uff, I've found the option. It is not under the special "Backcar setup", but simply in "Car infotament -> Video -> Reversible assistant lines". Anyway, it would be nice to have more options available like in Teyes.