C# set value in exe config such as remember password

static void SetConfig(string userName,string userPwd,string isRemembered)
{
Configuration cfg=ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
cfg.AppSettings["UserName"].Value=userName;
//string encryptedPwd=CipherHelper.Encrypt3DES(userPwd);
cfg.AppSettings.Settings["UserPwd"].Value=encryptedPwd;
cfg.AppSettings.Settings["IsRemebered"].Value="True";
cfg.Save(ConfigurationSaveMode.Modified,true);
ConfigurationManager.RefreshSection("appSettings");
}