how to update firebase document field angular

// how to create a collection
tutorials: Observable<any[]>;
// db: AngularFireStore
this.tutorials = db.collection('tutorials').valueChanges();

// To get meta data and create collection
tutorials: Observable<any[]>;
this.tutorials = db.collection('tutorials').snapshotChanges();

// how to add document to collection
const tutorialsRef = db.collection('tutorials');
const tutorial = { title: 'zkoder Tutorial', url: 'bezkoder.com/zkoder-tutorial' };
tutorialsRef.add({ ...tutorial });

// how to update a collection
const tutorialsRef = db.collection('tutorials');
tutorialsRef.doc('id').update({ title: 'zkoder new Tut#1' });

// how to delete a document in a collection
const tutorialsRef = db.collection('tutorials');
tutorialsRef.doc('id').delete();
updateDoc(_id: string, _value: string) {
  let doc = this.afs.collection('options', ref => ref.where('id', '==', _id));
  doc.snapshotChanges().pipe(
    map(actions => actions.map(a => {                                                      
      const data = a.payload.doc.data();
      const id = a.payload.doc.id;
      return { id, ...data };
    }))).subscribe((_doc: any) => {
     let id = _doc[0].payload.doc.id; //first result of query [0]
     this.afs.doc(`options/${id}`).update({rating: _value});
    })
}