Swift 4.0 - Firebase - after user logs in, I need firestore (firebase) to not use and store the random generated ID. I have this working on other pages in the iPhone app but not the main sign-in page. cannot get the syntax correct

*PLEASE NOTE, FIREBASE UI AND AUTHENTICATION ALREADY WORKS* 1) When user signs into Firestore (the backend database), its currently creating a new random generated ID as the document in the database (Firestore). This needs to save like the rest of the iPhone APP into a designated document (a folder in the DB) as the users email address rather than the random generated ID which is automatically assigned. Images attached. **TWO PAGES IN APP ALREADY HAVE THE DESIRED OUTCOME, 'Mention filter' and 'Create Filter' pages already save correctly and do not use the random generated ID in the database. I need the view controller 'MainVC' to complete the same thing when a user first authenticates. I cannot get the right syntax to work on the main page which is why I am looking for a freelancer to assist