Customize WooCommerce order notes placeholder and label

By default the label of “order notes” on WooCommerce checkout page is “Order notes”, and placeholder is “Notes about your order, e.g. special notes for delivery.”. This can be updated using woocommerce_checkout_fields filter.

Modify the placeholder and label as per your need, from the below code.

function careless_woo_custom_order_notes( $fields ) {
    $fields['order']['order_comments']['placeholder'] = 'Do you need any custom work done for your order?';
    $fields['order']['order_comments']['label'] = 'Customization';

    return $fields;
add_filter( 'woocommerce_checkout_fields', 'careless_woo_custom_order_notes' );

Code goes in the functions.php file of your active theme.