Undo and Redo Button in Kivy with Canvas

Question

Yesterday i Completed my Kivy Projects of a simple paint app and i give it to one of my friend and he told me that if You add Two Undo and Redo Buttons Then Your Application will Look Good and it will be more usable . But When I Try To Do It I Was Not Able To Do It i search a lot but i can't get any satisfying answer

Main Python File With Undo Button But No Function

from random import random
from kivy.app import App
from kivy.clock import Clock
from kivy.core.window import Window
from kivy.graphics import Color, Ellipse, Line
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.spinner import Spinner
from kivy.uix.widget import Widget


class MyPaintWidget(Widget):
    def on_touch_down(self, touch):
        self.d = MyPaintApp.sizeSpinner.text
        if MyPaintApp.colorSpinner.text == "Random Changing":
            color = (random(), random(), random())
        if MyPaintApp.colorSpinner.text == "Black":
            color = (0, 0, 0)
        if MyPaintApp.colorSpinner.text == "Red":
            color = (1, 0, 0)
        if MyPaintApp.colorSpinner.text == "Green":
            color = (0, 1, 0)
        if MyPaintApp.colorSpinner.text == "Blue":
            color = (0, 0, 1)
        if MyPaintApp.colorSpinner.text == "Pink":
            color = (1, 0, 1)
        if MyPaintApp.colorSpinner.text == "Sky Blue":
            color = (50/255.0, 150/255.0, 209/255.0)
        if MyPaintApp.colorSpinner.text == "Gray":
            color = (75/255.0, 82/255.0, 92/255.0)
        if MyPaintApp.colorSpinner.text == "White":
            color = (1, 1, 1)

        with self.canvas:
            Color(*color)
            Ellipse(pos=(touch.x - int(self.d) / 2, touch.y -int(self.d) / 2), size=(int(self.d), int(self.d)))
            if int(self.d)<=25:
                self.line = Line(points=(touch.x, touch.y), width=int(self.d)/3)
            else:
                self.line = Line(points=(touch.x, touch.y), width=int(self.d)/2.5)

    def on_touch_move(self, touch):
        self.line.points += [touch.x, touch.y]



class MyPaintApp(App):
    colorSpinner = Spinner(
        text="Black",
        values=["Random Changing", "Red", "Green", "Blue", "Black", "White", "Pink", "Gray", "Sky Blue"],
        font_size=20,
        background_normal="",
        background_color=(0, 0, 1, .75),
        bold=True,
        italic=True
    )
    sizeSpinner = Spinner(
        text="10",
        values=["5", "10", "15", "20", "25", "30", "35", "40", "45", "50"],
        font_size=20,
        background_normal="",
        background_color=(0, 1, 0, .75),
        bold=True,
        italic=True,
    )
    bgColor = Spinner(
        text="White",
        values=["White", "Red", "Green", "Blue", "Black", "Pink", "Gray", "Sky Blue"],
        font_size=20,
        background_normal="",
        background_color=(0, 0, 1, .75),
        bold=True,
        italic=True
    ) 

    undoBtn = Button(
        text="Undo",
        background_normal="",
        background_color=(1, 0, 1, .75),
        bold=True,
        italic=True,
        font_size=20
    )

    def __init__(self, **kw):
        super(MyPaintApp, self).__init__(**kw)
        Clock.schedule_interval(self.update, 1/60)


    def build(self):
        parent = BoxLayout(
            orientation="vertical"
        )
        self.painter = MyPaintWidget()
        bottom_bar=BoxLayout(size_hint=(1, .1))
        clearbtn = Button(
            text='Clear',
            bold=True,
            italic=True,
            font_size=24,
            background_normal="",
            background_color=(1, 0, 0, .75),
        )
        clearbtn.bind(
            on_release=self.clear_canvas
        )

        bottom_bar.add_widget(clearbtn)
        bottom_bar.add_widget(self.colorSpinner)
        bottom_bar.add_widget(self.sizeSpinner)
        bottom_bar.add_widget(self.bgColor)
        bottom_bar.add_widget(self.undoBtn)



        parent.add_widget(self.painter)
        parent.add_widget(bottom_bar)
        return parent

   def clear_canvas(self, obj):
       self.painter.canvas.clear()

   def update(self, dt):
        if self.bgColor.text == "Random Changing":
            Window.clearcolor = (random(), random(), random(), 1)
        if self.bgColor.text == "Black":
            Window.clearcolor = (0, 0, 0, 1)
        if self.bgColor.text == "Red":
            Window.clearcolor = (1, 0, 0, 1)
        if self.bgColor.text == "Green":
           Window.clearcolor = (0, 1, 0, 1)
        if self.bgColor.text == "Blue":
            Window.clearcolor = (0, 0, 1, 1)
        if self.bgColor.text == "Pink":
           Window.clearcolor = (1, 0, 1, 1)
        if self.bgColor.text == "Sky Blue":
            Window.clearcolor = (50/255.0, 150/255.0, 209/255.0, 1)
        if self.bgColor.text == "Gray":
            Window.clearcolor = (75/255.0, 82/255.0, 92/255.0, 1)
        if self.bgColor.text == "White":
            Window.clearcolor = (1, 1, 1, 1)


if __name__ == "__main__":
    app = MyPaintApp(title="PaintVerse: A Simple And Easy To Use Paint App")
    app.run()