Using Flutter Firestore plug in, do something for

To help me better understand Flutter and Firebase, I'm making a list sharing app. I'm working on the list home screen that will show a reorderable list tile view with a tile for each of the users' lists, I have not began to work on whats inside of these lists. I have firestore set up so that each list is a sub collection, now I want to create a tile for each sub collection in that user's document ( a list of that user's lists). I'm having a tough time telling flutter to do something for each sub collection without using a specific sub collection's name. I wanted to pass in a list title to each tile by making a collection reference for each sub collection( list) and calling .id on each one. Using the collection ID as the title, I'm not yet sure if I can do this or if ill have to make the list title a field inside of each list. Either way, I need to find out how to do something for each subcollection inside a particular document. .forEach seems to only work on document fields, not subcollections? What am I doing wrong? I'm sure there is a better way to go about this. I have not included any code as this is a big picture kind of question.

There is no method in the Firestore client-side SDKs to get all collections (or subcollections under a specific document). Such API does exist in the server-side SDKs, but not in the client-side SDKs.

See:

Fetching all collections in Firestore
How to get all of the collection ids from document on Firestore?

So you'll need to know the collections already, typically by changing your data model. For example by creating a document for each list's metadata, and then storing the list items in a subcollection with a known name under that document. That way you can get all lists by querying for the documents, which is possible within the API.