Expand the tools field on the left-hand side with the down arrow and then with the three points.
Press the symbol for Detour to show an alternative route with information about its longest/shortest route as well as calculated journey time. Normally only a short detour is proposed which quickly rejoins the original itinerary.
If the suggestion is accepted: Tap on the sign with detour information. The route is accepted even if you are driving on the road suggested. After the proposal is accepted, guidance is resumed - now with the detour selected as the route. If the suggestion is not accepted continue to drive on the original route.
An alternative to the Detour function is to diverge from the itinerary's route - the system then updates the route automatically and continues guidance to the destination along the most suitable route.
It is also possible to show an alternative route while driving continues.