Kivy Scrollview - how to reset scrollbar size?

Question

Noob here. I'm sure there is a simple solution to this but after hours of researching I can't seem to find the answer. I have a program that accepts input and returns the results to a Label in Kivy. The Label is a child of Scrollview. The problem I'm having is that when new input is entered the results are sent back to the Label to replace the previous results BUT the previous scrollbar doesn't reset to fit the size of the new returned results. So if the initial results are 10 lines long and the 2nd set of results are 100 lines long, the scollview only shows the first 10 results. Conversely if the 1st result is 100 lines long and the 2nd result is 10 lines long the 2nd results get placed in a container with a very long scrollbar and lots of empty space. Not ideal. Here's a sample of code that reproduces the issue I'm having.

Py Code:

from kivymd.app import MDApp
from kivy.lang import Builder


class MainApp(MDApp):

    def build(self):

        return Builder.load_file('testscroll.kv')

    def press_btn(self):
        
        self.root.ids.lbl1.text = "Hello There" * 500

    def press_btn2(self):
        self.root.ids.lbl1.text = "Howdy Back At Ya!"


MainApp().run()

KV File:

FloatLayout:
    BoxLayout:
        id: box1
        size_hint: 0.8, 0.8
        pos_hint: {"center_x": 0.5, "center_y": 0.5}
        spacing: dp(33)
        orientation: 'vertical'

        ScrollView:
            id: scroll1
            do_scroll_x: False
            do_scroll_y: True
            #size_hint: 1, None
            pos_hint: {'center_x': 0.5, 'center_y': 1}

            MDLabel:
                id: lbl1
                text: "Here we are!"
                text_size: self.size
                font_size: 18
                theme_text_color: "Custom"
                text_color: rgba('#f9a825')
                valign: "center"
                halign: "justify"   # justifies text in label box
                multiline: True
                pos_hint: {'center_x': 0.5, 'center_y': 0.5}
                size_hint_y: None
                height: self.texture_size[1]

        Button:
            id: btn
            text: "Change"
            on_release: app.press_btn()

        Button:
            id: btn2
            text: "Change 2"
            on_release: app.press_btn2()