How to update schema data in mongodb with mongoose and express

So I have a problem trying to work with mongodb. Firstly, I created a mongoose model like below which stores name.

const mongoose = require("mongoose");

const schema = new mongoose.Schema({
  name: {
    type: String
  },
 });
 
 mongoose.model("schema", schema);

And I posted a name. It looks like this in my mongodb compass.

{
  "_id": {
    "$oid": "628e0b35062e0d2e7fde17dc"
  },
  "name": "Bob",
}

Now I also want their age so I updated the model to this.

const mongoose = require("mongoose");

const schema = new mongoose.Schema({
  name: {
    type: String
  },
  age: {
    type: Number,
    default: 0
  }
 });
 
 mongoose.model("schema", schema);

The problem
The previous saved data at db doesnt have age property on it. I want previous registered name's age to be default to 0. New data will have the age property to them but not the previous data.