Before update:

I want update the value of Plavix 75mg:”50″. When user give a new value my code add a new value with a new ID instead of modifying the previous one. Here is the result:

Please help me to fix this.

Here is my code.

private void updatePharmaceutical(String documentId, String newDose, String newQuantity) {
    if (storeName != null) {
        CollectionReference storeCollection = db.collection(storeName);
        Map<String, Object> updates = new HashMap<>();
        updates.put("dose", newDose);
        updates.put("quantity", newQuantity);
        storeCollection.document(documentId).update(updates)
                .addOnSuccessListener(aVoid -> {
                    Toast.makeText(this, "Successfully updated.", Toast.LENGTH_SHORT).show();
                    updateRealtimeDatabase(documentId, newQuantity); // Update Realtime Database with new quantity
                })
                .addOnFailureListener(e -> Toast.makeText(this, "Error caught while updating document", Toast.LENGTH_SHORT).show());
    }
}

private void updateRealtimeDatabase(String drugName, String newQuantity) {
    FirebaseUser currentUser = FirebaseAuth.getInstance().getCurrentUser();
    if (currentUser != null) {
        String userId = currentUser.getUid();
        DatabaseReference userRef = FirebaseDatabase.getInstance().getReference("Pharmacists").child(userId).child("drugData");

        // Update Realtime Database with new quantity for the corresponding drug
        userRef.child(drugName).setValue(newQuantity)
                .addOnSuccessListener(aVoid -> Log.d("ViewPharmaceuticals", "Realtime Database updated with new quantity"))
                .addOnFailureListener(e -> Log.e("ViewPharmaceuticals", "Error updating Realtime Database", e));
    }
} 

I want to modify the same value instead of adding a new field. I tried so many ways to do this but every attempt was useless.