How to select all checkboxes and give that command to button in another class in Tkinter?

from tkinter import *
import tkinter as tk

class Win1(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        Label(self, text= "ISMC", font= ('Helvetica 20 bold')).pack(padx=5, pady=5)
        b1=Button(self, text="AUTO", command=lambda:controller.show_frame(Win2)).pack(padx=5, pady=5)

class Win2(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        b1=Button(self, text= "button 1", command=lambda:controller.show_frame(Win3)).pack(padx=5,      pady=5)
        b2=Button(self, text= "button 1").pack(padx=5, pady=5)
        b3=Button(self, text= "button 3").pack(padx=5, pady=5)
        b4=Button(self, text= "PROCEED").pack(padx=5, pady=5)
        b5=Button(self, text= "BACK", command=lambda:controller.show_frame(Win1)).pack(padx=5,  pady=5)

class Win3(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        val_x=0
        val_y=10
        self.vars = []
        self.array = []
        for i in range(3):
             self.array.append("RELAY " + str(i+1))
             self.vars.append(StringVar())
             self.vars[-1].set(0)
             c1=Checkbutton(self, text=self.array[i], variable=self.vars[-1], onvalue=1, offvalue=0).place(x=val_x, y=val_y)
             
             if i<=3:
                val_x=val_x+0
                val_y=val_y+50
                
        b1=Button(self, text="back", bg="red", fg="white", command=lambda:controller.show_frame(Win2)).place(x=30,y=140)
        b2=Button(self, text="proceed", bg="green", fg="white").place(x=30,y=160)
        b3=Button(self, text= "Select All").place()

class Application(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)
        window = tk.Frame(self)
        window.pack(side = "top", fill = "both", expand = True)
        self.frames = {}
        for F in (Win1, Win2, Win3):
            frame = F(window, self)
            self.frames[F] = frame
            frame.grid(row = 0, column=0, sticky="nsew")
        self.show_frame(Win1)
        
    def show_frame(self, window):
        frame = self.frames[window]
        frame.tkraise()
        self.title("Test") 
        self.geometry('1500x1500')
        
app = Application()
app.mainloop()       

I need to select all checkboxes in my window 3 and give that command to a button "AUTO" which is present in window 1. I tried many times but i don't know how to do that?

Can anyone please help. I am beginner of programming.