@kchaniyal,
There are a few ways to accomplish your task. One way can be via InsertRows method with InsertOptions parameter(s) regarding copy. So, you may insert your desired number of rows while copying the formatting (only) of the first row, then you may import data into those rows accordingly. See the sample code for your reference:
e.g.
Sample code:
Workbook workbook = new Workbook();
var style = workbook.CreateStyle();
var flag = new StyleFlag();
style.Font.IsBold = true;
flag.FontBold = true;
workbook.Worksheets[0].Cells.Rows[0].ApplyStyle(style, flag);
workbook.Worksheets[0].Cells[0, 0].PutValue("First Row we Created");//row, col
workbook.Worksheets[0].Cells.InsertRows(1,100,new InsertOptions() { CopyFormatType = CopyFormatType.SameAsAbove});//you may replace "100" with your desired number of rows.
workbook.Worksheets[0].Cells[1, 0].PutValue("Second Row we Created");// THIS TEXT will BE BOLD too.
workbook.Save("e:\\test2\\out1.xlsx");
Hope, this helps a bit.