'Documentreference' object has no attribute 'push'

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Python

NoSQL

I'm writing an app in Python that used Firestore/Firebase! I've got the database all set up. Now I've managed to add an account number into the database see below. Now each time the program runs it just writes over the already added account number! I don't know what to do!

doc_ref = db.collection(u'Clients').document(u'Teen Savings Account')
                doc_ref.set({
                    u'Account Number': accnumberr
                })

Here is what my database looks like! Database

What I have tried:

I've tried using push() so

doc_ref.push().set({...}) but it just gave me an error!