How to channge label text from tkinter?

Question

I'm trying to get the label called display to change the text whenever I press the button. My goal is, that it displays the value of gamer.trueCount, but I tried many approaches and I didn't manage to solve it. Could anyone help me?

from tkinter import *

#Constants
BUTTONWIDTH = 20
BUTTONHEIGHT = 10

LABELSIZE = 20

#Settings
DEFAULT_DECK_COUNT = 6

#DEFAULTFONT = ()


class util:
    def __init__(self):
        self.remainingDecks = 6
        self.runningCount = 0
        self.trueCount = 0
    
    def update(self):
        if(self.runningCount or self.remainingDecks) == 0: return
        else: self.trueCount = (self.runningCount/self.remainingDecks)
        print(self.trueCount)

    def add(self) -> None:
        self.runningCount += 1
        self.update()
        return
    
    def subtract(self) -> None:
        self.runningCount -= 1
        self.update()
        return

class Window(Frame):
    def __init__(self, master = None):
        Frame.__init__(self, master)
        self.master = master
        self.pack(expand = 1, fill = BOTH)

        display = Label(self, width=LABELSIZE, height=int(LABELSIZE/2), text=str(gamer.trueCount)).pack()

        addButton = Button(self, width=BUTTONWIDTH, height=BUTTONHEIGHT, text = "+", command= lambda : gamer.add()).pack()

        subtractButton = Button(self, width=BUTTONWIDTH, height=BUTTONHEIGHT, text="-", command= lambda : gamer.subtract()).pack()

root = Tk()
gamer = util()
app = Window(root)
root.mainloop()