main.py

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.button import Button
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.lang import Builder


class First_screen(Screen):
    pass


class Second_screen(Screen):
    pass


class My_manager(ScreenManager):
    pass


Builder.load_file("testing_screens.kv")


class Testing_screens(App):
    def build(self):
        return My_manager()


Testing_screens().run()

testing_screens.kv

<My_manager>:
    First_screen:
    Second_screen:

<First_screen>:
    name: "one"
    Button:
        text: "hello peeps"
        on_press: app.root.current= "two"

<Second_screen>:
    name: "two"
    Button:
        text: "world gurus"
        on_press: app.root.current= "one"

Thank you, man

Thank you, I wish that I had found your example hours ago.