Magento 2: Extend place order mutation

Question

I have tried this Magento2/vendor/magento/module-quote-graph-ql/etc/schema.graphqls

type Mutation {
placeOrder(input: PlaceOrderInput): PlaceOrderOutput @resolver(class: "\\Magento\\QuoteGraphQl\\Model\\Resolver\\PlaceOrder")
}

input PlaceOrderInput {
    cart_id: String!
    anonymousId: String
}

Request:

mutation {
  placeOrder(
    input: {
      cart_id: "6tGj0vqL9VZ5FhyIySaHSIUaqmEFbyHm",
      anonymousId: "6tGj0vqL9VZ5FhyIySaHSIUaqmEFbyHm"
    }
  ) {
    order {
      order_number
    }
  }
}

But its not working with error Unknown argument "anonymousId" on field "placeOrder" of type "Mutation