I want to add discount by click on custom button in Add-to-cart page.

Hello everyone, I want to add discount by click on custom button in Add-to-cart page. But it’s not happening. How can I do that?? Below is my code that I have added in theme functions.php:

function add_content(){
     
        if(isset($_POST['takeway'])) {
            // Call Recalculate function
            add_action( 'woocommerce_after_calculate_totals', 'woocommerce_after_calculate_totals', 30 );
        } 
    ?> 
    <form method="post"> 
        <input type="submit" name="takeway" value="Takeway"/> 
    </form>

<?php

}
add_action('woocommerce_cart_coupon', 'add_content');

// Recalculate Function       
function woocommerce_after_calculate_totals( $cart ) {

    global $woocommerce;
    $subtotal = $woocommerce->cart->get_subtotal();
    $discount = 40/100;
    $cart->total = $subtotal*$discount;

}