Please find below code to change coupon code message.

function woocommerce_rename_coupon_message_on_checkout() {
return ‘ <a href=”#” class=”showcoupon”>’ . __( ‘Have a promotional code?’, ‘woocommerce’ ) . ‘</a>’;
}
add_filter( ‘woocommerce_checkout_coupon_message’, ‘woocommerce_rename_coupon_message_on_checkout’ );

/* Remove successfully add to cart message */

add_filter( ‘wc_add_to_cart_message’, ‘__return_empty_string’ );