Hi,
The function REGEX_REPLACE was added in MySQL 8.0.4. You must be using an older version of MySQL.
Unfortunately, with old versions of MySQL there is no regex replacement functions so you can't use this.
In that case, you can try instead to use a "run PHP code" action with the code:
$db = JFactory::getDBO();
$name = preg_replace('#^[0-9]+\-#','', '{product_name}');
$db->setQuery('UPDATE #__hikashop_product SET product_name =' . $db->Quote($name).' WHERE product_id = {product_id}');
$db->execute();
That will do the same but got through PHP to run the regex before doing the MySQL query from the PHP code.