I have found the program might not recognize segment lines as darts. To get round this, use the Edit Pattern Tool and left click the legs of the dart. Right click and from the drop down menu select, "Shape dart cap" > enter. It is now recognized as a dart. Now with the Edit Pattern Tool again, select the dart and right click, "Rotate Dart" should be available.
I have found the program might not recognize segment lines as darts. To get round this, use the Edit Pattern Tool and left click the legs of the dart. Right click and from the drop down menu select, "Shape dart cap" > enter. It is now recognized as a dart. Now with the Edit Pattern Tool again, select the dart and right click, "Rotate Dart" should be available.