When building a custom route that returns to the same starting point then your custom route will be saved for you to use again on the return journey. For example, if you are going from Ellerman House to 78on5th in Hermanus and back to Ellerman House using a custom route both ways.
To reverse your custom route, select 'Self Drive (No Route)' for the return journey. This will default to a straight line between the two points where you can select the vehicle icon to load the existing custom route.