I think the OP’s route is taking other roads in addition to LA37. If that is the case, an additional point or two will need to be added to the route. Select the route in the lower left pane and choose the Insert editing tool (looks like a pencil). As you move the cursor close to the route, a thick gray line will appear your start and end points. When it appears click the left mouse button once. You should see thin lines connecting the route points to the cursor. Add a point somewhere along LA 37 with a left mouse click. A good place would be ca. half way between the missing segment of LA 37, but not too close to an obvious connection to the undesired route.
You may have to add more than one point. The tool will be ready to add another point closer ahead of the one you made. If you need to add a point behind, press the esc key and select a different segment to edit (the thick gray line mentioned above) by approaching the route between the start point and the new point.