在python中按下按钮后如何更新按钮文本？

我正在尝试制作一个最终能够得分的应用程序。我要解决的一个问题是如何以某种方式按下或更新按钮后的文本。我是python / kivy的新手。我发现了几个类似的问题，涉及函数等，但是没有一个涉及.kv文件和单独的窗口。我的代码如下。

main.py

import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen

class MainWindow(Screen):
    pass

class ScoreWindow(Screen):
    pass

class WindowManager(ScreenManager):
    pass

kv = Builder.load_file("mainkv.kv")


class MyMainApp(App):
    def build(self):
        return kv

if __name__ == "__main__":
    MyMainApp().run()

主kv

WindowManager:
    MainWindow:
    ScoreWindow:

<MainWindow>:
    name: "main"

    GridLayout:
        cols: 1

        Button:
            text: "Quick Score"
            on_release:
                app.root.current = "score"
                root.manager.transition.direction = "left"

<ScoreWindow>:
    name: "score"

    GridLayout:
        cols: 7
        Button:
            name: "three"
            text: "Press to Update"
            on_release:
                three.text = "Updated"

        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: "Score"
            on_release:
                app.root.current = "main"
                root.manager.transition.direction = "right"
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: ""
        Button:
            text: "Go Back"
            on_release:
                app.root.current = "main"
                root.manager.transition.direction = "right"