Rename WooCommerce checkout field label & placeholder

woo_rename_checkout.php

// WooCommerce Rename Checkout Fields
add_filter( 'woocommerce_checkout_fields' , 'custom_rename_wc_checkout_fields' );

// Change placeholder and label text
function custom_rename_wc_checkout_fields( $fields ) {
$fields['billing']['billing_first_name']['placeholder'] = 'Wonka';
$fields['billing']['billing_first_name']['label'] = 'Your Awesome First Name';
return $fields;
}