# ChangeLabelText.py
from tkinter import *
master = Tk()
master.geometry("200x100")

#---Variables---
my_var = StringVar()


#---Functions---
def change_text():
    my_var.set("Second click")


my_var.set("First click")
label = Label(master,textvariable=my_var, fg="black")
label.grid(column=0, row=0)
button = Button(master,text="Click Me",command = change_text)
button.grid(column=0, row=1)

master.mainloop()