Usually we would not recommend restarting the game because you will lose all of your previous progress and in-app purchases.
However if you would like to start again follow these steps:
1. Delete the game from your device
2. Re-download the game from your app store
3. Launch the game
4. If the data selection popup appears, select the option at Level 0
However if you would like to start again follow these steps:
1. Delete the game from your device
2. Re-download the game from your app store
3. Launch the game
4. If the data selection popup appears, select the option at Level 0