De-register woocommerce checkout js and register new
<?php
add_action( 'wp_enqueue_scripts', 'tt_wp_enqueue_scripts_for_custom_checkout', 99 );
function tt_wp_enqueue_scripts_for_custom_checkout(){
if( is_checkout() ){
// Checkout Page
wp_deregister_script('wc-checkout');
wp_register_script('wc-checkout', get_template_directory_uri() . "/js/tt-checkout.js",
array( 'jquery', 'woocommerce', 'wc-country-select', 'wc-address-i18n' ), '2.3.13', TRUE);
wp_enqueue_script('wc-checkout');
}
}
?>