Hi there.
I have no idea how to do that differently than writing it in the forum, forbidding a turn seems simple enough to me that I should be able to do it myself, or at least find an easy way to report the issue directly in the map editor. Here is the issue:
Coming from Biograd na moru on my way to Crkvine info point on Vransko jezero the navigation suggests a left turn from D8 at the intersection with Kneza Trpimira unto an unnamed road. That left turn is forbidden, as you can see even from the satellite image.
If someone can tell me whether there is an easier way to report such an issue, please let me know as well 
Hvala
Thanks for the report, we will correct it