Woocommerce Update the product skus with the number that is gathered from the Product Title. In this example SKU is in parentheses in Product Title.

functions.php

<?php

// Update the product skus with the number that is gathered from the Product Title. SKU is in parentheses
// Make it available as an admin page
function update_product_skus() {
    $args = array(
        'post_type' => 'product',
        'posts_per_page' => -1,  // Retrieve all products; adjust if needed
    );

    $products = get_posts($args);

    foreach ($products as $product) {
        $title = $product->post_title;

        if (preg_match('/\((\d+)\)/', $title, $matches)) {
            $number = $matches[1];
			echo $number . '<br>';
            update_post_meta($product->ID, '_sku', $number);
        }
    }

    echo "Completed updating SKUs.";
}

add_action('admin_menu', 'register_my_custom_menu_page');

function register_my_custom_menu_page(){
    add_menu_page(
        'Update SKUs', 
        'Update SKUs', 
        'manage_options', 
        'update-skus', 
        'update_product_skus'
    );
}