Can't figure out how to delete document from Firestore.

Inside PopMenuButton I am unsuccessfully trying access postID by doing the following:

onSelected: (value) async {
            await FirebaseFirestore.instance.collection('thread').doc(FBCloudStore.  ).delete();
            //await FBCloudStore.deletePostInFirebase(postID);
          },

Here is my FBCloudStore, where I think I need to change something.