update tb_RHContratos
set DtCadastro = cast(DtCadastro as datetime)

SELECT *
FROM tb_RHContratos
WHERE isdate(DtCadastro) = 0

SELECT DtCadastro,
    CASE WHEN TRY_CAST(DtCadastro AS datetime) IS NOT NULL
    THEN 'Ok'
    ELSE 'Falhou'
AS "Resultado da Conversão"
FROM tb_RHContratos