Why in the Sedra Nasso Chapter 7 Verses 12-84 it is repeated the same offerings from each tribe. Why does Torah repeat in detail these gifts from each tribe and why are the gifts the same?

While there is no simple answer to this question, the repetition suggests that each Nasi, while performing the exact same rituals as the one before him, did it as if he was the first, with his own original intentions (see midrash for a wide variety of interpretations of the symbolism of the offerings) and his own excitement and devotion. For further explanation you can chaeck the Ramban.