Flutter/Firebase-How to show data of two collections in a third separate collection?

I am making an app in which user requests to book a butcher or make order for some amount of meat. I have two classes.

1. BookingRequests (through which I see booking requests of all users from booking_collection)
2. OrderRequests (through which I see order requests of all users from order_collection)

The code of both is almost similar. One displays a ListView of X-Animal slaughtering booked. The other displays X-Animal meat ordered. There is an IconButton in both. I want if I press the icon button either class data should be saved in a third collection approved_requests. I am new to flutter. Can anyone help me in doing so? Here is the code of booking.dart

 class BookingRequests extends StatelessWidget {
  final db = Firestore.instance;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView(
        children: <Widget>[
          StreamBuilder<QuerySnapshot>(
              stream: db.collection('booking_collection').snapshots(),
              builder: (context, snapshot) {
                if (snapshot.hasData) {
                  return Column(
                    children: snapshot.data.documents.map((doc) {
                      return ListTile(
                            title: new Text(
                                  "${doc.data['animal']} slaughtering booked",
                                ),
                            trailing: IconButton(
                              icon: Icon(Icons.done),
                              onPressed: (){
                                //implementation here
                              },
                            ),
                      );
                    }).toList(),
                  );
                } else {
                  return SizedBox();
                }
              }),
        ],
      ),
    );
  }
}

Similarly my order.dart

class OrderRequests extends StatelessWidget {
  final db = Firestore.instance;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView(
        children: <Widget>[
          StreamBuilder<QuerySnapshot>(
              stream: db.collection('order_collection').snapshots(),
              builder: (context, snapshot) {
                if (snapshot.hasData) {
                  return Column(
                    children: snapshot.data.documents.map((doc) {
                      return ListTile(
                            title: new Text(
                                  "${doc.data['animal']} meat ordered",
                                ),
                            trailing: IconButton(
                              icon: Icon(Icons.done),
                              onPressed: (){
                                //implementation here
                              },
                            ),
                      );
                    }).toList(),
                  );
                } else {
                  return SizedBox();
                }
              }),
        ],
      ),
    );
  }
}