Use the Modify Item Promotion window to set up promotions (enter items, set the promotion price, assign a start and end date, and so on). You can also use this window to modify existing promotions. Changes can be made on an individual basis by clicking a field in the grid. Or you can select the option to make global changes from the Misc menu. Global changes allow you to enter a change once and have it applied to all items on the promotion.
Tip: You can set up Eagle Alerts for when promotions start and end. See options 3311 and 3313 in the topic "Setting Up Eagle Alerts Options."