The static method FXMLLoader.load returns the root node (and so the objet hierarchy) defined in the .fxml file. In your case it seems to be an AnchorPane.
Your fist line should be
AnchorPane root = FXMLLoader.load(SampleController.class.getResource("settings.fxml"));
Use this object to construct your new scene, for example
Scene trial_scene = new Scene(root, 300, 300, Color.BLACK);
Then pass this scene to your new stage
m.setScene(trial_scene);