Step 1: From the admin dashboard, navigate to Products > All Products.
Step 2: Select the product you want to set the quantity discount
Step 3: At the Product data section, select tab Quantity Based Pricing
Step 4: Enable the Quantity discount feature then choose the Discount type as a percentage and fixed amount
Step 5: If you select the Intervals rule, you can set the min and max quantity that visitors have to buy to get the discounts.
If you select the Steps rule, when the quantity is a multiply of the step, then the discount will be applied.