Convert Varchar column to Date without losing the data

Question

Before the database was saving the date in a varchar field and in the Brazilian standard (dd/mm/YYYY), then I modified the values using the code below:

UPDATE tabela SET coluna= DATE_FORMAT(STR_TO_DATE(coluna, '%d/%m/%Y'), '%Y-%m-%d')
WHERE coluna LIKE '__/__/____';

At that point it worked perfectly, stayed in the pattern YYYY-mm-dd, but when changing from varchar to date it ended up erasing all my data and filling with 0000-00-00.