JavaFX - How To Open Multiple FXML Windows

I'm making a tic tac toe program. Currently I have a welcome screen for my tic tac toe game, once the button is clicked I want the main game to open. I have created two FXML VBox windows created from JavaFX Scene Builder. I want to know how to close the welcome menu and launch the 2nd FXML window.

This 2nd FXML window will have it's own controller where the tic tac toe calculations will be held.

Here is the event listener on when the mouse action is performed on the button

@FXML
private void startGame(ActionEvent event) {
}