How can i access a control in mvvm model in viewmodel?

 Grid grid = new Grid();
            grid = App.Current.Windows[1].FindName("grid1") as Grid;
            if (grid != null)
            {
                RowDefinition rd = new RowDefinition();
                rd.Height = GridLength.Auto;
                grid.RowDefinitions.Add(rd);
                TextBox txt = new TextBox();
                txt.Name = "txtNewAdd";
                txt.Height = 23;
                txt.VerticalAlignment = VerticalAlignment.Top;
 
                //txtFname is in view Layer
                TextBox txtName = new TextBox();
                txtName= grid.FindName("txtFname") as TextBox;
                if (txtName!=null)
                {
                    txt.Background = txtName.Background ;
                    
                }
                Grid.SetColumn(txt, 1);
                Grid.SetRow(txt,(grid.RowDefinitions.Count-1));
                
                grid.Children.Add(txt);
            }