merge two excel files to dataGridView for different column name and n

check it

private void button1_Click(object sender, EventArgs e)
{
    int row = 0;
    string[] ListFiles = Directory.GetFiles(@"C:\Users\User Name\Documents\ttt", "*.xlsx", SearchOption.AllDirectories);
    foreach (string filename in ListFiles)
    {
          Excel.Application xlApp = new Excel.Application();
          Excel.Workbook xlWorkbook = xlApp.Workbooks.Open(filename);
          Excel._Worksheet xlWorksheet = xlWorkbook.Sheets[1];
          Excel.Range xlRange = xlWorksheet.UsedRange;
          int rowCount = xlRange.Rows.Count;
          int colCount = xlRange.Columns.Count;
          dataGridView1.ColumnCount = 2;
          //iterate over the rows and columns and print to the console as it appears in the file
          //excel is not zero based!!
          for (int i = 1; i <= rowCount; i++)
          {
               string[] colstring = {"",""}; // two columns
               for (int j = 1; j <= colCount; j++)
               {
                    //new line
                    if (j == 1)
                         Console.Write("\r\n");
                    //write the value to the console
                    if (xlRange.Cells[i, j] != null && xlRange.Cells[i, j].Value2 != null)
                    {
                         Console.Write(xlRange.Cells[i, j].Value2.ToString() + "\t");
                         Console.WriteLine(j);
                         colstring[j-1] = xlRange.Cells[i, j].Value2.ToString();
                    }
                }
                dataGridView1.Rows.Add(colstring);
           }
           //cleanup
           GC.Collect();
           GC.WaitForPendingFinalizers();
           // rule of thumb for releasing com objects:
           // never use two dots, all COM objects must be referenced and released individually
           // ex: [somthing].[something].[something] is bad
           //release com objects to fully kill excel process from running in the background
           Marshal.ReleaseComObject(xlRange);
           Marshal.ReleaseComObject(xlWorksheet);
           //close and release
           xlWorkbook.Close();
           Marshal.ReleaseComObject(xlWorkbook);
           //quit and release
           xlApp.Quit();
           Marshal.ReleaseComObject(xlApp);
     }
     print_datagridview();
}
private void print_datagridview()
{
     for (int rows = 0; rows < dataGridView1.Rows.Count; rows++)
     {
          Console.Write("\n");
          for (int col = 0; col < dataGridView1.Rows[rows].Cells.Count; col++)
          {
              if ( dataGridView1.Rows[rows].Cells[col] != null)
              {
                   if ( dataGridView1.Rows[rows].Cells[col].Value != null)
                   {
                        string value = dataGridView1.Rows[rows].Cells[col].Value.ToString();
                        Console.Write(value + "\t");
                   }
              }
          }
     }
}