Prerequisite: You have added an intent into your Dialogflow agent with the action 'firebase.update'
Once you create a suitable intent, you are ready to trigger the intent and cause the intent to call the webhook, which is turn will write the data to the Cloud Firestore.
Once you have declared the intent with a suitable action, you can simply type a phrase from your userSays phrase into your Dialogflow console.
Now go to your Firebase console and check to see if the data has been updated:
Does it work as expected?
Congratulations. You have successfully implemented your first update from your Dialogflow agent to your Cloud Firestore.
The steps are quite similar if you simply wish to use the real time database instead of the Cloud Firestore, obviously with some changes to the code that accesses the data.