How to restart a new game after account was bound?

Go to the settings menu and the Account option, the same as you did to bind your game. Near the bottom is the option to 'Start a new game'.

Once you have reach a point in the new game that you can also bind it. Make sure to bind to a different external account (make a new IM30 account for example). You can then use the 'Switch Account' option on the same screen to log in to either of your games.