Update nested value in mongoDB document

Question

I've a document called cart, inside on a user document where I want to update the quantity value if the item is already present.

document:

{
  "_id": {
    "$oid": "614b72a9a6c2dd5aa95ee03e"
  },
  "name": "Mainak",
  "email": "mainakdas104@gmail.com",
  "cart": {
    "items": [
      {
        "productId": {
          "$oid": "614b771a6d33c02b74c669b7"
        },
        "quantity": 1
      }
    ]
  }
}

How do I iterate over the array, find and update the value of quantity ?

I'm using mongo-db npm driver.