If you add a new waypoint on an existing route, the dashboard will consider this waypoint to be the last waypoint by default and hence will not modify the existing route but rather extend it.
You will be able to add a new waypoint on top of the existing route. You can drag and drop it where you would need so that the route is edited accordingly.
You can add upto 100 waypoints in a single route.
You can also delete a waypoint by
tapping on it and then clicking on "X" icon.