Configuring a button (or any widget) in Tkinter is done by calling a configure method
“config”
To change the size of a button called button1 you simple call
button1.config( height = WHATEVER, width = WHATEVER2 )
If you know what size you want at initialization these options can be added to the constructor.
button1 = Button(self, text = "Send", command = self.response1, height = 100, width = 100)