simple excel template.cs

// Compose Data
Dictionary<string, object> data = new Dictionary<string, object>();
data["NAME"] = "Takuya Sawada";
data["GENDER"] = "Male";
data["BIRTH"] = new DateTime(1989, 3, 3).Date;
data["TODAY"] = DateTime.Today.Date;
data["LEVEL"] = 99;

// Render template
XLWorkbook workbook = new XLWorkbook(@"C:\Users\takuya\Desktop\template.xlsx");
IXLWorksheet sheet = workbook.Worksheet("Sheet1");

foreach (IXLNamedRange nr in workbook.NamedRanges)
{
    if (data.ContainsKey(nr.Name))
    {
        workbook.Cell(nr.Name).Value = data[nr.Name];
    }
}

// Save
workbook.SaveAs(@"C:\Users\takuya\Desktop\takuya.xlsx");