Resetando os índices e renomenado a coluna dos ativos

cotacoes = cotacoes.reset_index().rename(columns={'level_1': 'Ativo'})

Organizando o df

cotacoes = cotacoes[["Date", "Open", "High", "Low", "Close", "Ativo"]]

apos essas rodarem certo

KeyError                                  Traceback (most recent call last)
<ipython-input-18-51ad5c67136e> in <cell line: 2>()
      1 # Organizando o df
----> 2 cotacoes = cotacoes[["Date", "Open", "High", "Low", "Close", "Ativo"]]

2 frames
/usr/local/lib/python3.10/dist-packages/pandas/core/indexes/base.py in _raise_if_missing(self, key, indexer, axis_name)
   6131 
   6132             not_found = list(ensure_index(key)[missing_mask.nonzero()[0]].unique())
-> 6133             raise KeyError(f"{not_found} not in index")
   6134 
   6135     @overload

KeyError: "['Ativo'] not in index"