You can't. There are no dead ends in the game, and therefore there is no need, and no way, to restart on the same account. Don't worry - even if you make some mistakes in the beginning, you always have the chance to catch up with your enemies and maybe even surpass them! A good tip is to fulfill the tasks in the exact order in which they are given. Any deviation and you can use up your Resources too quickly and possibly slow down your development. If this happens, just wait until you produce enough Resources to continue.