Ref:

Export data from SQL Server to Excel in ASP.Net using C# and VB.Net

You can rename your DataTable column names. Refer this code

protected void ExportExcel(object sender, EventArgs e)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT * FROM Customers"))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    //Added these line Start
                    dt.Columns[0].ColumnName = "ID";
                    dt.Columns[1].ColumnName = "UserName";
                    dt.Columns[2].ColumnName = "Location";
                    //Added these line End
                    using (XLWorkbook wb = new XLWorkbook())
                    {
                        wb.Worksheets.Add(dt, "Customers");

                        Response.Clear();
                        Response.Buffer = true;
                        Response.Charset = "";
                        Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
                        Response.AddHeader("content-disposition", "attachment;filename=SqlExport.xlsx");
                        using (MemoryStream MyMemoryStream = new MemoryStream())
                        {
                            wb.SaveAs(MyMemoryStream);
                            MyMemoryStream.WriteTo(Response.OutputStream);
                            Response.Flush();
                            Response.End();
                        }
                    }
                }
            }
        }
    }
}