Last marker isnt connected with a route after deleting a route in between

Question

The code here is to delete gmaproutes and markers based on the index given in my numericupdown box. When I have like 4 markers and gmaproutes , and I want to delete the 2nd gmaproute and marker, the 3rd gets connected to the 1st but the 4th is left unconnected with any other markers. How can I make all markers to be connected even after deleting a marker/gmaproute in between?

private void button4_Click(object sender, EventArgs e)
        {

            int row_index = (int)numericUpDown1.Value - 1;

            if (row_index >= 0 && row_index < dt.Rows.Count)
            {
                dt.Rows.RemoveAt(row_index);
                if (row_index < o.Markers.Count)
                    o.Markers.RemoveAt(row_index);


                if (row_index < line_overlay.Routes.Count)
                {

                    for (int i = line_overlay.Routes.Count - 1; i >= row_index; i--)
                               {
                                    line_overlay.Routes.RemoveAt(i);

                                }
                                if (row_index > 0 && row_index < o.Markers.Count)
                                {
                                    
                                    PointLatLng lastMarkerPos = o.Markers[row_index - 1].Position;
                                    PointLatLng nextMarkerPos = o.Markers[row_index].Position;   
                                    
                                    GMapRoute newRoute = new GMapRoute(new List<PointLatLng>()

                            {

                                lastMarkerPos,
                                nextMarkerPos
                            }, "New Route");
                                    newRoute.Stroke = new Pen(Brushes.Blue, 2);

                                    
                                    line_overlay.Routes.Insert(row_index, newRoute);
                                    
                    }


                            }

                        }
                
                for (int i = row_index; i < dt.Rows.Count; i++)
        {
            dt.Rows[i]["Marker"] = i + 1; 
        }
    

            if (row_index > dt.Rows.Count)
            {
                row_index = dt.Rows.Count;
                numericUpDown1.Value = row_index + 1;
            }

            if (dt.Rows.Count == 0)
            {
                ClearAll();
            }
        }

I tried adding another gmaproute with an index of row_index+1 but that doesn't seem to fix it