Fill your washing machine with cold water.
Place 1 to 4 scoops of powdered stain remover in the water. Refer to the directions on the powdered stain remover packaging. For instance, it might suggest 1 scoop for small loads and 4 scoops for extra large loads.
Add your normal laundry detergent. Powdered stain remover is not a laundry detergent. Powdered stain remover manufacturers recommend adding detergent along with their product. Add detergent as per the instructions on the detergent packaging based on the load size.
Allow the white sheets to soak for 1 to 6 hours.
Launder the sheets on the normal cold water cycle.
Inspect the sheets to see if they are again white. If they are still stained or yellow. repeat the process until they are white.