When you want to apply a discount to a number of products, you don't need to use the sale product-by-product, bulk action helps you to apply the same sale on many products at the same time.
In order to apply sale by bulk follow the steps below:
1. Navigate to Catalog on the left sidebar.
2. Open Products and choose the store where you want to add sales.
3. Select the products which need to be discounted, open the Bulk Action, and choose Add Sales.
Tip: You can filter the needed product using the catalog search.
4. Now choose the needed sale and click Apply.
Now all the checked products have the sale. Learn more about operating sales here.