You can add the following sql command in your database using PHP my admin or anyother DB editor
Update wp_postmeta Set meta_value="instock" Where meta_value="outofstock" And meta_key = '_stock_status'
You can add the following sql command in your database using PHP my admin or anyother DB editor
Update wp_postmeta Set meta_value="instock" Where meta_value="outofstock" And meta_key = '_stock_status'