Click the information button "i" and then "Report an Issue".
There is no "i" button from the navigation screen and there's no "i" button from the search results either if you want to report entirely irrelevant results.
This is likely an intentional design decision, and it sounds like a common-sense safety feature.
Great feature for walking and public transit directions. They still have interactive bits for the driving directions — I can't imagine what sort of "common sense" simply hides the report a problem thing until you dig through a few levels of mediocre UI.
There is no "i" button from the navigation screen and there's no "i" button from the search results either if you want to report entirely irrelevant results.