How to delete documents that contain a certain value in one of the fields. Firestore, Flutter

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I have these documents, which contain data about each task I add to the list in my app.

child: StreamBuilder(
stream: _tasks.snapshots(),
builder: (context, AsyncSnapshot<QuerySnapshot> streamSnapshot) {
if (streamSnapshot.hasData) {
return ListView.builder(
itemCount: streamSnapshot.data!.docs.length,
itemBuilder: (context, index) {
final DocumentSnapshot documentSnapshot =
streamSnapshot.data!.docs[index];
return GestureDetector(
onLongPress: () => _update(documentSnapshot),
child: ListTile(
)
);
},
);
}

return const Center(
child: CircularProgressIndicator(),
);
},
),

I am using a stream builder to build the list. Each of the tasks have a checkmark and when i click it, It updates the value in firestore inside the IsDone field accordingly. I want to click a button outside the stream builder to delete the checked tasks. How do I loop through all the documents and find all the documents that contain the value true and delete them?

I tried this but im doing doing something wrong and it isnt changing anything:

  void _delete() {
    var docs = _tasks.doc().snapshots();
    docs.forEach((doc){
      if(doc.data()==true){
        _tasks.doc(doc.id).delete();
      }
    });
    ScaffoldMessenger.of(context).showSnackBar(const SnackBar(
        content: Text('You have successfully deleted a product')));
  }