https://woocommerce.com/products/storewide-sale-for-woocommerce/
Storewide Sale for WooCommerce allows you to enable sales for multiple products in bulk. You can set the storewide sale as a percentage or fixed reduction and specify the start and end dates of the sale. It’s time consuming to add sale prices to products individually. This extension allows you to put bulk products on sale with a single click.
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