How the Setting File Automatically Update?

[KiddoV]

I have a basic config file:

{
  "app": {
    "general": {
      "isMaxWindow": true
    },
    "advance": {
      
    }
  }
}

When I update the value:

viper.Set("app.general.isMaxWindow", false)

The file is not update. How do I make it update just for that value?
In other word, how do I make the file automatically update whenever I change the any value by .Set() method?