TROUBLE PROGRAMING A 20% DISCOUNT ON MY CASH...

Question

I HAVE THE MANUAL THAT SAYS YOU CAN PROGRAM A 20% DISCOUNT ON THE REGISTER AS WELL AS A MARKUP BUT IT IS ONLY ALLOWING ME TO DO A MARK-UP & I JUST CAN SEEM TO FIGURE OUT HOW TO WORK ON THE DISCOUNT PART , I DONT NEED THE MARK-UP? DO YOU THINK YOU CAN SOLVE THE PROBLEM FOR ME?