ConfigurationManager.AppSettings как после изменения обновить значения в файле

ConfigurationManager.AppSettings["ServerNameDB"] = this.tbServerDB.Text;
                ConfigurationManager.AppSettings["CatalogDB"] = this.tbCatalogDB.Text;
                ConfigurationManager.AppSettings["UsersDB"] = this.tbUserNameDB.Text;
                ConfigurationManager.AppSettings["PasswordDB"] = this.tbPasswordDB.Text;
                ConfigurationManager.AppSettings["ConnectTimeout"] = this.tbConnectionTimeoutDB.Text;
                ConfigurationManager.AppSettings["PatchController"] = this.tbPatchController.Text;
                ConfigurationManager.AppSettings["PatchControllerCellVerification"]=this.tbPatchControllerCellVerification.Text;

  private static void Save(string configKey, string value)
        {
            if (ConfigurationManager.AppSettings[configKey] != value)
            {
                Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
                AppSettingsSection asSection = config.AppSettings;
                asSection.Settings.Remove(configKey);
                asSection.Settings.Add(configKey, value);
                config.Save();
                ConfigurationManager.RefreshSection(asSection.SectionInformation.Name);
            }
        }

ConfigurationManager.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");

//Create the object
Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
 
//make changes
config.AppSettings.Settings["Username"].Value = txtUsername.Text;
config.AppSettings.Settings["Password"].Value = txtPassword.Text;
 
//save to apply changes
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");

ConfigurationManager.Save(ConfigurationSaveMode.Modified);