If you want to start the game from the beginning you need to create new account and use it.

 

To create new account follow the instruction below:

1. Turn off Game Center in device settings.
2. Create a new Apple ID. https://support.apple.com/en-us/HT204316#ios
3. Log in with this Apple ID in the device settings.
4. Enable Game Center in device settings.
5. Launch game.
6. After the loading screen, a sync indicator will appear in the lower left corner of the screen.
7. If a green checkmark appears, then the new account has been successfully synchronized.