How to bind an interface to functions in PySimpleGUI

I have a next files: https://github.com/Greenboyisyourdream/PasswordGenerator

How can i do to make the "generate" button execute the function on line 12 in the app.py

(The function on line 12 in the app.py):

elif button == "Generate!":
    screen.format()
    screen = str(*[random.choice(list(symbols)) for _ in range(lenght)])
    window.FindElement("output").Update(screen)