Send a notification in app to another user using Firebase Messaging given user's device token in Flutter

Question

I came across Firebase Messaging, and after reading through the guide, they have posted here: https://firebase.google.com/docs/cloud-messaging/flutter/client, I was able to get a user's device token. However, the tutorial only presents an example of sending a test message to a device using the Firebase console. How would I send a notification to another user given the (other user's) device token from within a flutter app? Is there a function I can run that takes the device token and notification body that I am unaware of?

Locution