Registers GTIN field from Product GTIN for WooCommerce plugin as a pre-population option.

functions.php

<?php

/**
 * Registers a meta field as a prepopulation option.
 */
function lw_woocommerce_gpf_custom_field_list( $list ) {
	$list['meta:_wpm_gtin_code'] = 'GTIN field from Product GTIN for WooCommerce plugin';

	return $list;
}

add_filter( 'woocommerce_gpf_custom_field_list', 'lw_woocommerce_gpf_custom_field_list' );