Change order of search in woocommerce
<?php
add_filter('woocommerce_get_catalog_ordering_args', 'ywcas_woocommerce_catalog_orderby');
function ywcas_woocommerce_catalog_orderby( $args ) {
$args['orderby'] = 'meta_value';
$args['order'] = 'asc';
$args['meta_key'] = '_sku';
return $args;
}