Как поменять картинку кнопки, при наведении на неё

Попробуйте так:

from tkinter import *

class MyButton(Button):
    def __init__(self, master, **kwargs):
        Button.__init__(self, master=master, **kwargs)
        
        self.defaultImage = self["image"]
        self.bind("<Enter>", self.on_enter)
        self.bind("<Leave>", self.on_leave)

    def on_enter(self, e):
        self.Activ = PhotoImage(file='images\Help.png')
        self['image'] = self.Activ

    def on_leave(self, e):
        self['image'] = self.defaultImage

root = Tk()

photoImage = PhotoImage(file='images\Ok.png')
myButton = MyButton(root, image=photoImage)
myButton.grid()

root.mainloop()