如何在Kivy中按下另一个屏幕中的按钮时更改屏幕中的标签文本

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button
from kivy.uix.label import Label

class MyScreen(Screen):
    def __init__(self, **kwargs):
        super(MyScreen, self).__init__(**kwargs)
        
        # 创建标签和按钮
        self.label = Label(text="默认文本")
        self.button = Button(text="更改文本", on_press=self.change_label_text)
        
        # 将标签和按钮添加到屏幕中
        self.add_widget(self.label)
        self.add_widget(self.button)
        
    def change_label_text(self, instance):
        self.label.text = "新的文本"

sm = ScreenManager()
sm.add_widget(MyScreen(name='screen1'))

class MyApp(App):
    def build(self):
        return sm

if __name__ == '__main__':
    MyApp().run()