If you want to reset your savegame and start from the beginning, on Android you can do this by deleting the data & cache of the app through your device settings. You can also uninstall the game, and reinstall the game (this works for both: Android & iOS).

If you were connected with Google Play Games or Game Center, after starting a new savegame, it may prompt you to select which savegame you want to use. You can either select the local savegame (your cloud savegame will be overwritten), or you can just log out from your cloud account, and it won't be overwritten, while you continue playing with the local account.

Notice that by deleting the app data (or reinstalling the game), all progress will be deleted and only the permanent purchases (if applicable) will be restored with on your new savegame!