One of the ways to do that is,

Set the final destination,

then go to advanced planning and add a waypoint, if you select an address or point on the map on the other road it will then take you that way instead.

An exaggerated example would be,

LA to NY, TT wants you to go Via Tulsa because it is the shortest route, but you want to visit friends in Omaha.
So, set the destination as NY then add a waypoint for Omaha and it will work out the best route to do that and will ignore Tulsa.

I hope that makes sense.