How can I clean a yellowish silicone mobile back cover and prevent it from yellowing again?

Is there a way to get rid of this or do I need to buy new one?

[![](https://i.stack.imgur.com/Lt4Iu.jpg)](https://i.stack.imgur.com/Lt4Iu.jpg)

[![](https://i.stack.imgur.com/fjNRb.jpg)](https://i.stack.imgur.com/fjNRb.jpg)

Can see how yellowish it is become.