How do you change the value of a text element already defined in a .fxml file in JavaFX

Currently, I'm making a client-side anime streamer(pls no bully), and currently learning JavaFX. I've created a static thumbnail, and I need to change the value of the static content. So, how do you change the value of a text element already defined in a .fxml file in JavaFX?

For reference, here's the code.

videoThumbnail.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.*?>
<?import javafx.scene.image.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.text.*?>

<AnchorPane prefHeight="387.0" prefWidth="243.0" style="-fx-background-color: #000000;" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="test.gui.Controller">
   <children>
      <ImageView fitHeight="266.0" fitWidth="184.0" layoutX="36.0" layoutY="26.0" pickOnBounds="true" preserveRatio="true">
         <image>
            <Image url="@../images/mL0215_1024x1024.png" />
         </image>
      </ImageView>
      <Label layoutX="36.0" layoutY="308.0" style="-fx-background-color: #000000;" text="My Hero Acadamia" textFill="WHITE">
         <font>
            <Font name="System Bold" size="17.0" />
         </font>
      </Label>
   </children>
</AnchorPane>

main.java

    @Override
    public void start(Stage primaryStage) throws Exception {
        try {
            FXMLLoader loader = new FXMLLoader(getClass().getResource("/fxml/videoThumbnail.fxml"));
            Pane root = (Pane) loader.load();
            Scene scene = new Scene(new Group(root));

            primaryStage.setTitle("test");
            //root.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
            primaryStage.setScene(scene);
            primaryStage.show();

            letterbox(scene, root);
            primaryStage.setFullScreen(true);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        launch(args);
    }

Controller.java

package test.gui;

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.input.MouseEvent;

public class Controller {
}

The normal procedure would be to define the static part of your UI in FXML (e.g. place an ImageView onto a Pane) and then add the dynamic part (e.g. changing the image inside the ImageView) in your code. That's what the Controller is meant for.