title: Convert integer to datetime in pandas dataframe
body: <p>I used
  <code>pd.to_numeric (df['dates'], downcast = 'integer')</code>
  to convert a datetime64 to int64 but if I want to convert it back to datetime format, what should I do?
  Earlier it was in format: 2020-02-19 but after conversion it is now 1582070400000000000. I can't find a way to revert it back to datetime64.</p>