My realtime Firebase database

[![enter image description here](https://i.stack.imgur.com/bV38H.png)](https://i.stack.imgur.com/bV38H.png)

I try to change position for many lat langs at some time like cars in uber, 
but when I change lat or lang or both this don't change the position of marker but its make anew marker. I want when lat for example is changed in realtime database the markers also changed based on the value of that lat 

I try make condition 

```
`if (marker != null) 
    setPosition 
 else "marker == null"` 
    add new marker 

```

but the problem is I have >1 markers so that this solution is display me on the map one marker only because marker != null 

```
public class Map extends FragmentActivity implements OnMapReadyCallback {
FirebaseDatabase database;
DatabaseReference myRef;
GoogleMap mMap;
MarkerOptions options;
Marker mCurrLocationMarker;
LatLng ll;
model save;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_map);
    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);
}

  @Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;

    database = FirebaseDatabase.getInstance();
    myRef = database.getReference("user");

    myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot ds : dataSnapshot.getChildren()) {

                Double lang = ds.child("lang").getValue(Double.class);
                Double lat = ds.child("lat").getValue(Double.class);
                save = new model(lat, lang);
                ll = new LatLng(save.getLat(), save.getLang());

                mCurrLocationMarker = mMap.addMarker(options
                        .position(ll));

            }

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

```

I expected the marker's position was changed when I change real time lat and lang in firebase, but the result is created another marker.