How do I to change the property value for custom datagridviewcomboboxcell

[ToolboxItem(false)]
 public class MCCBEditingControl : MultiColumnsComboBox, IDataGridViewEditingControl
 {
     private DataGridView _DataGridView;

     public MCCBEditingControl()
     {
     }
     public DataGridView EditingControlDataGridView
     {
         get { return _DataGridView; }
         set { _DataGridView = value; }
     }

     private int rowIndex;
     public int EditingControlRowIndex
     {
         get { return rowIndex; }
         set { rowIndex = value; }
     }

     protected override void OnSelectedValueChanged(EventArgs e)
     {
         try
         {
             EditingControlValueChanged = true;
             this.EditingControlDataGridView.
                 NotifyCurrentCellDirty(true);
             base.OnSelectedValueChanged(e);
         }
         catch (Exception)
         {

             throw;
         }
     }

     public object EditingControlFormattedValue
     {
         get
         {
             if (this.SelectedIndex > 0)
             {
                 return this.Text.ToString();
             }
             else if (this.SelectedIndex == 0)
             {
                 //Show MessageBox Option to add new item
                 return string.Empty;
             }
             else
             {
                 return string.Empty;
             }
         }
         set
         {
             string newValue = value as string;
             if (newValue != null)
                 this.Text = newValue;
         }
     }

     private bool valueChanged = true;
     public bool EditingControlValueChanged
     { get => valueChanged; set => valueChanged = value; }

     public Cursor EditingPanelCursor =>
         base.Cursor;

     public bool RepositionEditingControlOnValueChange => false;


     public void ApplyCellStyleToEditingControl(
         DataGridViewCellStyle dataGridViewCellStyle)
     {
         this.Font = dataGridViewCellStyle.Font;
         this.ForeColor = dataGridViewCellStyle.ForeColor;
         this.BackColor = dataGridViewCellStyle.BackColor;
     }

     public bool EditingControlWantsInputKey(
         Keys keyData, bool dataGridViewWantsInputKey)
     {
         // Let the DateTimePicker handle the keys listed.
         switch (keyData & Keys.KeyCode)
         {
             case Keys.Left:
             case Keys.Up:
             case Keys.Down:
             case Keys.Right:
             case Keys.Home:
             case Keys.End:
             case Keys.PageDown:
             case Keys.PageUp:
             case Keys.Enter:
                 return true;
             default:
                 return false;
         }
     }

     public object GetEditingControlFormattedValue(
         DataGridViewDataErrorContexts context)
     {
         return EditingControlFormattedValue;
     }

     public void PrepareEditingControlForEdit(bool selectAll)
     {

     }

     protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
     {
         if (keyData == Keys.Tab || keyData == Keys.Enter)
         {
             this.DroppedDown = false;

             if (this.SelectedIndex == 0)
                 return true;
         }
         return base.ProcessCmdKey(ref msg, keyData);
     }


 }

public class MCCoboBoxCell : DataGridViewComboBoxCell
{
    public override Type EditType => typeof(MCCBEditingControl);

    public override Type ValueType => base.ValueType;

    public MCCoboBoxCell() : base()
    {
    }

    public override void InitializeEditingControl(
        int rowIndex, object initialFormattedValue,
        DataGridViewCellStyle dataGridViewCellStyle)
    {
        base.InitializeEditingControl(
            rowIndex, initialFormattedValue, dataGridViewCellStyle);

        MCCBEditingControl ctl=
            DataGridView.EditingControl as MCCBEditingControl;

        ctl.ShowAddNew = true;
        ctl.NewButtonText = NewItemButtonCaption;
        ctl.DropDownStyle = ComboBoxStyle.DropDown;
    }

    public override object DefaultNewRowValue =>
        base.DefaultNewRowValue;

    private string _NewButtonText ="Add New";

    public string NewItemButtonCaption
    {
        get
        {
           return _NewButtonText;
        }
        set
        {
            _NewButtonText = value;
        }
    }
    public static List<MCCoboBoxCell> mCCoboBoxCells = new List<MCCoboBoxCell>();
    public override object Clone()
    {
        var clone = (MCCoboBoxCell)base.Clone();
        clone.NewItemButtonCaption = this.NewItemButtonCaption;
        mCCoboBoxCells.Add(clone);
        return clone;
    }

}

public class MultiColumnComboBox : DataGridViewComboBoxColumn
{
    public MultiColumnComboBox()
    {
        this.CellTemplate = new MCCoboBoxCell();
    }

    private string _NewButtonText = "Add New Account";

    [NotifyParentProperty(true)]
    public string NewItemButtonCaption
    {
        set
        {
            _NewButtonText = value;
            Clone();
            foreach (MCCoboBoxCell cell in MCCoboBoxCell.mCCoboBoxCells)
            {
                cell.NewItemButtonCaption = this.NewItemButtonCaption;
            }
        }
        get
        {
            return _NewButtonText;
        }
    }
    public static List<MCCoboBoxCell> mCCoboBoxCells = new List<MCCoboBoxCell>();
    public override object Clone()
    {
        var clone = (MCCoboBoxCell)base.CellTemplate;
        clone.NewItemButtonCaption = _NewButtonText;
        mCCoboBoxCells.Add(clone);
        return base.Clone();
    }

}