In the instance that a driver notices an incorrect sign-posted speed in SmartNav: Navigation, they can update request using the app on their iFace.
...
From the navigation screen:
Tap this button 
Tap "Map error":
And report the speed limit error
, tap the button down the bottom right corner
Tap Wrong speed limit
Tap Send
This report is sent directly to the map provider, Here.com, who will assess the request, based on the location at the time that the Send button is tapped.
Please note that updates can take a minimum of 6 months to be pushed out.