Testing JSON key and then writing nested values to existing JSON file

I have a changes.json file which has directives as key value pairs i.e. "action": "add" that I wish to test and depending on that test to then read in the payload to an array and update a source.json file. First here is the format of the original source JSON file. There are three sections to test, users, playlists, and songs.

{
    "users" : [
      {
        "id" : "1",
        "name" : "Albin Jaye"
      }
    ],
    "playlists" : [
      {
        "id" : "1",
        "owner_id" : "2",
        "song_ids" : [
          "8",
          "32"
        ]
      }
    ],
    "songs": [
      {
        "id" : "1",
        "artist": "Camila Cabello",
        "title": "Never Be the Same"
      }
    ]
  }

And then the changes.json file that has the action directive to tell the code how to process, i.e. update, delete, add, etc

{
    "users": [{
        "action": "add",
        "payload": [{
                "id": "1",
                "name": "Albin Jaye"
            },
            {
                "id": "2",
                "name": "Dave Mustaine"
            }
        ]
    }],
    "playlist": [{
        "action": "add",
        "payload": [{
            "id": "1",
            "owner_id": "2",
            "song_ids": [
                "8",
                "32"
            ]
        }]
    }],
    "songs": [{
        "action": "add",
        "payload": [{
            "id": "1",
            "artist": "Camila Cabello",
            "title": "Never Be the Same"
        }]
    }]
}

Here is the code I have so far. First section I am able to iterate over the JSON and test the key by a switch:

Object.entries(data).map(([key, [{ action, payload }]]) => { 
    console.log(key, [{action, payload}]);
                    
    switch (key) {
        case 'users':
        // How to test for "add":"action"???
        // How to read in nested "payload"
        // How to update source JSON file with this value?
        break;
                        
    }
});

And for one of the tests/part, I have this code that reads through key/value pairs and pushes to array, but not sure about a couple of things.

const array = [];

    for (const [key, value] of Object.entries(data)) {
        if (data[key] === 'payload') {
            array.push([`${key}`, `${value}`]);
        }
    }
    console.log(array)
    // after reading into array, how to update source.json file with new data?

1. How to test for the "action":"add" key/value once I test for "user" node. This is probably just a syntax thing? data[user.action]?

2. Once tested, how to take the payload key/values and munge/update them back into the source.json`` file? I am guessing JSON.stringify(array) => fs.write(target)“` or something similar?

Thanks everyone!