We enter a product, and scroll to the “Product data” section.
The product can be simple or variable.
If it is simple
All we have to do is enter the new price in the Price Reduced field.
We have the possibility to assign a time to the discounted price by clicking on Schedule, (to the right of the discounted price field) and setting the start and end date.
In the Variations tab we will have the variants of this product, in this case sizes, which will have a price field each.
If we click on one of them we will have, like the simple product, the normal price and the discounted price. Also the possibility of assigning a schedule.