WooCommerce Total Tax Amount Update in Checkout Page

Question

I want to change total tax amount in the checkout page and my code is below.

function change_tax_for_checkout_page( $cart ) {
    $cart->set_total_tax(20);//20USD
    $check =  $cart->calculate_totals();
    return $cart;
}

add_action( 'woocommerce_before_checkout_form', 'change_tax_for_checkout_page' );

But it's not working.