Flutter: Edit an existing item using provider - flutter

Question

I am creating an app that works like so.
User creates a report EquipmentReport and on that report, they can add a list of AdditionalWN via a form called NotificationForm
The user should be able to add / delete and change any of the AdditionalWN items on the report
As the AdditionalWN is quite a complex model, I have implemented a ChangeNotifier on both the EquipmentReport and the AdditionalWN
EquipmentReport
class EquipmentReport extends ChangeNotifier {
List<AdditionalWN> _notifications;
List<ReportImage> _imgs;
List<bool> _inspectionResultSelectedStates;
String _locationIDVerification;
String _inspectionComments;
UnmodifiableListView<AdditionalWN> get notifications => UnmodifiableListView(_notifications);
void addNotification(AdditionalWN notification) {
_notifications.add(notification);
notifyListeners();
}
void removeRemoveNotification(AdditionalWN notification) {
_notifications.remove(notification);
notifyListeners();
}
.........
AdditionalWN
class AdditionalWN extends ChangeNotifier {
String _id = UniqueKey().toString();
String _notificationText = '';
String _notificationTitle = '';
int _isFault = 1;
int _isBreakdown = 0;
int _isWorkComplete = 0;
int _probabilityOfFailure = 0;
int _consequencePeople = 0;
int _consequenceEnvironment = 0;
int _consequenceReputation = 0;
int _consequenceAsset = 0;
int _equipmentID = 0;
String get id => _id;
int get equipmentID => _equipmentID;
set equipmentID(int value) {
_equipmentID = value;
notifyListeners();
}
String get notificationText => _notificationText;
set notificationText(String value) {
_notificationText = value;
notifyListeners();
}
String get notificationTitle => _notificationTitle;
set notificationTitle(String value) {
_notificationTitle = value;
notifyListeners();
}
..........
Adding a new AdditionalWN to the report is working fine using this button on the EquipmentReport where I pass a new instance of the ChangeNotifierProvider<AdditionalWN> to my NotificationForm()
ElevatedButton(
child: Text('Add'),
onPressed: () {
Navigator.of(context).push(
//here we create a new instance of the AdditionalWM and change provider to send to the new page
MaterialPageRoute(
builder: (BuildContext context) => ChangeNotifierProvider<AdditionalWN>(
create: (context) => AdditionalWN(),
builder: (context, child) => NotificationForm(),
),
),
);
},
)
Where I am struggling is how do I let me user edit an existing AdditionalWN?
Currently when a user clicks the edit button on the list of AdditionalWNs they get an error.
A AdditionalWN was used after being disposed.
Once you have called dispose() on a AdditionalWN, it can no longer be used.
The relevant error-causing widget was
NotificationForm
Here is my code to allow them to navigate to the NotificationForm
ListTile(
leading: IconButton(
onPressed: () {
Navigator.of(context).push(
//here we need to pass an existing model and change provider using ChangeNotifierProvider.value so we can edit
MaterialPageRoute(
builder: (BuildContext context) => ChangeNotifierProvider.value(
value: model.notifications[index],
child: NotificationForm(),
),
),
);
},
icon: Icon(Icons.edit),
),
I'm really lost on how to be able to pass both a new AdditionalWN to the NotificationForm as well as an exsiting AdditionalWN to the same NotificationForm