Quote: "Can anyone give me some advice to improve the game? the game is not selling well now."
I'm sure the game itself is fine. You just need to focus on the advertising now. A video on Youtube (a short gameplay teaser or even a trailer in general) would be a good place to start. Doesn't have to stop at Youtube, either. You can post the same teaser on Dailymotion, Vimeo, etc. Make your game go viral. Get people to know that your game is actually there ready for purchase in the App Store.
You may even consider looking into
Kickstarter. It's another great way to get your game out there, and you can even ask funding to help with the advertising.
Kravenwolf