To enable Promotional Pricing go to the Settings > Product Settings menu. Select Edit then under the Pricing section select Enable Promotional Pricing  

Next select Save at the top right of the screen

With this option selected, under a Product a Promotions tab will display

Select this tab then +Add. This will display fields for setup of a specific Promotional Price.

Select the Price Level, a Start and End Date. Pricing Method options are Fixed Price, Percentage above cost and Percentage below selling price. Enter the corresponding Fixed Rate or Percentage value.  

A Promotional Price cannot be setup if its date range overlaps with an already setup Promotional Price.

Once all required data is entered select Save.

Import Export

An Import & Export is available for Promotional Pricing from under the ...More Options menu of the Product List screen.   

• Importing matching dates will update pricing. 
• Importing different dates will be checked to ensure there is no overlap with old pricing.