You need to find a good trainer to help with this! Look for a balanced trainer, preferably with extensive GSD experience! Believe me, while hiring a trainer is not real expensive, it's not cheap either. But it's priceless in terms of how quickly your puppy will become manageable, and how much they can help you understand your puppy!
It's not the size of the dog in the fight, it's the size of the fight in the dog. Mark Twain