从一个接口下载了csv文件，中文全部乱码了，怎么恢复正常啊，我在header里已经设置UTF8编码了

wx.downloadFile({
      url: url,
      method: 'GET',
      header: {
        "cookie": cookie,
        "Content-Type": 'charset=UTF-8'
      },
      success: function (res) {
        var tempFilePath = res.tempFilePath;
        console.log(res);
        wx.saveFile({
          tempFilePath: tempFilePath,
          success: function (res) {
            var savedFilePath = res.savedFilePath;         
          },
        })
      },
    })