Husham,
It should be as simple as swapping the order that the stops are added to the selectedLocations array in the _routeSelectedLocations function in the items-list.js file in the widget folder.
currently is has this:
selectedLocations.push(this._getPointFromGeometry(this._selectedPoint.geometry));
selectedLocations.push(this._getPointFromGeometry(this._selectedFeature.geometry));
If you add reverse:
selectedLocations.push(this._getPointFromGeometry(this._selectedPoint.geometry));
selectedLocations.push(this._getPointFromGeometry(this._selectedFeature.geometry));
selectedLocations.reverse();
Then it should get you what you want.