Update A screen in kivy

Question

Hi i am writing a program for my uncles business where he can scan barcodes to keep inventory, im jsut trying to get the part where he can see what all is in his inventory and i have ran into a issue where i need to update a screen when i click on a button so i can see the updated text file how would i go about this?

python file:

class HomeScreen(Screen):
    pass

class ViewBarcode(BoxLayout):
    pass

class Scroll(ScrollView):
    pass

class Stack(StackLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        f = open(f'{cwd}/items/items.txt', 'r')
        lines = f.readlines()

        for i in lines:
            b1 = Button(
                text=str(i),
                size_hint=(1, None),
                size=(200, dp(50)),
            )
            b1.bind(on_press=self.button1)
            self.add_widget(b1)

    def button1(self, instance):
        id = (instance.text).replace('\n', '')
        f = open(f'{cwd}/items/{id}.txt', 'r')
        lines = f.readlines()
        print(instance.text)
        print(f'''Item Name: {lines[0]}\nPrice: {lines[1]}''')
        f = open(f'{cwd}/depends/temps.txt', 'w')
        f.write(str(id))
        f.close()
        App.get_running_app().root.current = 'ViewItem'

class ViewItemScreen(Screen):
    f = open(f'{cwd}/depends/temps.txt', 'r')
    lines = f.readlines()
    barcode = lines[0]
    f = open(f'{cwd}/items/{barcode}.txt', 'r')
    lines = f.readlines()
    name = lines[0]
    price = lines[1]
    name = lines[0]

class barcode(App):
    def build(self):
        sm = ScreenManager()
        sm.add_widget(HomeScreen(name='HomeScreen'))
        sm.add_widget(ViewItemScreen(name='ViewItem'))
        return sm


barcode().run()

.kv file

HomeScreen:

<HomeScreen>:
    BoxLayout:
        cols:2
        BoxLayout:
            cols:2
            size_hint: .5,1
            orientation: 'vertical'
            TextInput:
                size_hint: 1,1
                text: 'Enter Barcode'
                multiline: False
                on_text_validate: pass
            Button:
                #size_hint: .5,1
                text: 'hi'
        Scroll:
            size_hint: .5,1
            Stack:
                size_hint: 1,None
                height: self.minimum_height


<ViewItemScreen>:
    ViewBarcode:
        BoxLayout:
            size_hint:.25,1
            BoxLayout:
                orientation: 'vertical'
                Button:
                    text: 'home'
                    size_hint: .25,.25
                    on_press: root.manager.current = 'HomeScreen'
                #Label:
                #    size_hint: .25,.75
            BoxLayout
                orientation: 'vertical'
                TextInput:
                    text: root.barcode
                TextInput:
                    text: root.name
                TextInput:
                    text: root.price
            Label
                size_hint: .25,1