Usando o Kivy Screen Manager, crio duas telas. Enquanto estiver na tela 1, quero alterar um rótulo na tela dois. Destaco a área problemática no meu código:

meutest.ky:

#: import ScreenManager kivy.uix.screenmanager.ScreenManager
#: import Screen kivy.uix.screenmanager.ScreenManager
#: import SettingsScreen screen


ScreenManager:
    MenuScreen:
    SettingsScreen:


<MenuScreen>:
    name: 'MenuScreen'
    BoxLayout:
        Button:
            text: 'Goto nn'
            on_press: 
                root.manager.current = 'SettingsScreen'
                root.change_text()


<SettingsScreen>:
    name: 'SettingsScreen'
    label_id: label_field
    BoxLayout:
        Label:
            id: label_field
            text: "to_be_changed"

e meuscreen.py

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.screenmanager import ScreenManager, Screen


class MenuScreen(Screen):
    def change_text(self):
        pass
        # HERE: something like
        # root.SettingsScreen.label_field.text = 'new text'


class SettingsScreen(Screen):
    pass


class TestApp(App):
    pass

TestApp().run()

Qualquer ajuda é muito apreciada! Obrigado Nico