File | Settings | IDE Settings | JavaFX
Specify where the JavaFX Scene Builder executable file is located. If you do so, you'll be able to open your FXML files in the Scene Builder right from within IntelliJ IDEA.
|Path to SceneBuilder||
Specify the path to the JavaFX Scene Builder executable file.
Type the path in the field, or click (Shift+EnterShift+EnterShift+EnterShift+EnterShift+EnterShift+EnterShift+EnterShift+EnterShift+EnterShift EnterShift EnterShift Enter) and select the Scene Builder executable file in the dialog that opens.