To start the game from the beginning, you need to sign in to Game Center with an Apple ID that is not currently linked to your game progress.
This can be either:
a newly created Apple ID, or
an existing Apple ID that has never been used with this game.
Follow these steps:
Open Settings on your device.
Tap Game Center.
Sign out of your current Game Center account.
Sign in to Game Center using a different Apple ID (or create a new one if needed).
Apple’s guide to creating a new Apple ID: https://support.apple.com/en-us/HT204316#ios
Make sure Game Center is enabled after signing in.
Launch the game.
After the loading screen, a sync indicator will appear in the lower-left corner of the screen.
When a green checkmark appears, the new account has been successfully synchronized and the game will start from the beginning.