There are a lot of suggestions on the net for that. I have tried them all pretty much and none of them last long. The only one worth a damn is make a paste of baking soda and sparkling water. About 2 tablespoons of each. Wash your case really well with dish soap first then with a cheap toothbrush scrub the paste mix on the inside and outside of the case. Put a good layer on it and let it sit 10 minutes. Then rinse it off really well. Dry it completely. It will look better. I gave up on clear cases. None of them stay clear.