How to Cloud Firestore Data Sort by Desc SwiftUI

I am trying to fetch the data from my Firestore collection and now what i want to do is to sort the documents by one of the fields say "dateCode" Attaching codes below:

func getDescOrderData(completion: @escaping ([String:Any]) -> Void) {
    var dictInfo = [String:Any]()
    Firestore..collection("OldData").order(by: "dateCode", descending: true)
        .whereField("dateCode", isLessThanOrEqualTo: “Mon”)
        .whereField("studentId", isEqualTo: self.studentId)
        .getDocuments { (querySnapshot, error) in
            if let error = error {
                print("Old History Data error: \(error.localizedDescription)")
                return
            }
            if let snapshot = querySnapshot {
                for document in snapshot.documents {
                        dictInfo.append(document.data())
                }
                completion(dictInfo)
            }
        }
}

But i got error given below:-

Old History Data error: The query requires an index. You can create it here: https://console.firebase.googl.................

Any help would be greatly appreciated.