Hema HN7

We've got a HN7 and downloaded the Hema maps onto our PC. The idea is to plan routes using the bigger screen and send details of the planned trip to other members of the party.
I have worked out how to plot a route on the map but if a mistake is made (missing a turn-off) I can't erase the mistake. Hema doesn't answer my calls so I was wondering if anyone out there can help me.
Simply put, if I make a mistake while route plotting how can I delete the unwanted part of the plot.
As an aside, I am able to erase the whole route plot - no issues.
Cheers
Simon