Ok, I doubt anyone on here will know this, but given a neutral tannakain category there is a bijection between this category and the representations of some group (with some adjectives). I'm not sure how to show that, don't care though. But, to recover the group from the category of representations you look at the automorphisms of the forgetful functor from the category of representations of the the group to the vector space created by the representations of the group. How exactly do you recover the group from the automorphisms of the forgetful functor? Illustrate this with an example.