How do I use the Tub Clean cycle to maintain the dishwasher?

Remove all dishes from the appliance, add 3 tablespoons (40 g) of citric acid to the detergent dispenser (do not use dishwasher detergent), and run the Tub Clean (Download Cycle: P1) cycle by pressing START. Run this cycle once a month or after every 30 cycles to eliminate residual soil, odor, white spots, and other dirt inside the appliance. (Page 39)