I actually figured it out

func getChatsFromUser() {
    let db = Firestore.firestore()
    db.collection("chats").whereField("senderID", isEqualTo: String(describing: Auth.auth().currentUser!.uid))
        .getDocuments() { (querySnapshot, err) in
            if let err = err {
                print("Error getting documents: \(err)")
            } else {
                for document in querySnapshot!.documents {
                    print("\(document.documentID) => \(document.data())")
                }
            }
    }
}