i watch color change from pink

First, no such thing as an iWatch, I'm guessing that you are referring to the Apple Watch. Next, what are you asking about changing, the case color? If so, then the only way to get a different case color is to purchase a different watch. The return period for the Apple Watch is 14 days. If after that, you would need to sell the device and use the proceeds of that sale to help purchase a new device with the color case you wish.