How to export two grids in a single worksheet of a workbook in WinForms GridGroupingControl?

//Creating custom class
public class GridGroupingExcelConverterControlEXT: GridGroupingExcelConverterControl
{
    private int rowIndex = 1;
    public GridGroupingExcelConverterControlEXT()
    {
    }
    public int ExcelStartRowIndex { get { return rowIndex; } set{ rowIndex = value; } }
    protected override void ExportTable(IList tableElements, GridTableDescriptor tableDescriptor, ref int excelRowIndex, int excelStartColumnIndex,bool isNestedTable,IWorksheet sheet,ExcelExportingOptions exportingOptions)
    {
        excelRowIndex = ExcelStartRowIndex;
        base.ExportTable(tableElements, tableDescriptor, ref excelRowIndex, excelStartColumnIndex, isNestedTable, sheet, exportingOptions);
    }
}
//Exporting to Excel
private void exportBtn_Click(object sender, EventArgs e)
{          
    ExcelEngine Engine = new ExcelEngine();
    IWorkbook workbook = Engine.Excel.Workbooks.Create(1);
    IWorksheet sheet = workbook.Worksheets[0];
    sheet.Name = "sample";                    
    ExcelExportingOptions options = new ExcelExportingOptions();
    GridGroupingExcelConverterControlEXT converter = new GridGroupingExcelConverterControlEXT();
 
    //Exporting 1st grid
    converter.ExportToExcel(gridGroupingControl1, sheet, options);
 
    //Specifying the starting row index of 2nd grid
    converter.ExcelStartRowIndex = sheet.UsedRange.LastRow + 2;
 
    //Exporting 2nd grid
    converter.ExportToExcel(gridGroupingControl2, sheet, options);
    workbook.SaveAs("Sample.xls");
    Process.Start("Sample.xls");
}

'Creating custom class 
Public Class GridGroupingExcelConverterControlEXT
     Inherits GridGroupingExcelConverterControl
     Private rowIndex As Integer = 1
     Public Sub New()
     End Sub
     Public Property ExcelStartRowIndex() As Integer
         Get
 Return rowIndex
         End Get
         Set(ByVal value As Integer)
 rowIndex = value
         End Set
     End Property
     Protected Overrides Sub ExportTable(ByVal tableElements As IList, ByVal tableDescriptor As GridTableDescriptor, ByRef excelRowIndex As Integer, ByVal excelStartColumnIndex As Integer, ByVal isNestedTable As Boolean, ByVal sheet As IWorksheet, ByVal exportingOptions As ExcelExportingOptions)
          excelRowIndex = ExcelStartRowIndex
          MyBase.ExportTable(tableElements, tableDescriptor, excelRowIndex, excelStartColumnIndex, isNestedTable, sheet, exportingOptions)
     End Sub
End Class
 
'Exporting to Excel
Private Sub exportBtn_Click(ByVal sender As Object, ByVal e As EventArgs) Handles exportBtn.Click
     Dim Engine As New ExcelEngine()
     Dim workbook As IWorkbook = Engine.Excel.Workbooks.Create(1)
     Dim sheet As IWorksheet = workbook.Worksheets(0)
     sheet.Name = "sample"
     ' save to workbook in excel
     Dim options As New ExcelExportingOptions()
     Dim converter As New GridGroupingExcelConverterControlEXT()
 
    ‘Exporting 1st grid
    converter.ExportToExcel(gridGroupingControl1, sheet, options)
    ‘Specifying the starting row index of 2nd grid
    converter.ExcelStartRowIndex = sheet.UsedRange.LastRow + 2
 
    ‘Exporting 2nd grid
    converter.ExportToExcel(gridGroupingControl2, sheet, options)
    workbook.SaveAs("Sample.xls")
    Process.Start("Sample.xls")
End Sub