01) Access the Control Panel
02) After login click on Catalog >> Multiple Product Administration
03) Access the category and / or subcategory
04) Select products
At the bottom select the option: Add on Promotion
Fill in the promotion field as per example
Please select an expiration date
05) After clicking on the CONFIRM button
Video: https://www.youtube.com/watch?v=mz3n6UjN-l8&feature=youtu.be