If you wish to use a route during your ride, before the start of the activity go to the details page of the desired route and click on the “Start with this route” button.
If the route has been created from BikeCompanion, then you benefit from turn by turn navigation and voice instructions.
Automatic route replanning can be activated in the“Other” menu, then“User preferences”.
You can also create a route ‘on the fly’ while recording an activity. See the documentation here.