For some reason you want to restart the game again. (Remember though that this will also erase all progress, you can go back and replay old levels). If you are really sure you want to do that.. (a small part of me thinks why?! Why would you!? Some levels I never want to see again ever ever ever!)
You have two options.
The quickest option is to uninstall the game. Reboot your device. Reinstall the game.
When it comes to logging in, either use an account that hasn't been registered with the game (or any other player) and log in with that. If you haven't a new account, make one. Its important to make an account to save progress. Facebook only allow you to have one account under their terms and conditions, so it might be best to make a Kingdom account. You can find out how to do that here.
If you would rather use the same account that you have now, it may be possible for the King team to erase progress, but you would have to contact them directly. Follow this blog post and you will find the contact link to do so on there. Make sure you choose gameplay/progress so it gets to the right department
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