很久以前有做一個依照excel template set value的功能，可以參考看看
source code

我是用OpenXml來複製現有的Excel工作表, 然後在新工作表修改【值】。

using (var memoryStream = new MemoryStream())
{
                //用Openxml複製工作表
                using (var workbook = new XLWorkbook(HttpContext.Current.Server.MapPath("~/App_Data/範本.xlsx")))
                {
                    workbook.SaveAs(memoryStream);

                    //用Openxml複製
                    using (SpreadsheetDocument doc = SpreadsheetDocument.Open(memoryStream, true))
                    {
                        WorkbookPart workbookPart = doc.WorkbookPart;

                        var dd = query.StartDate.Date; //報表查詢起日
                        while (dd <= query.EndDate.Date)
                        {
                            //複製的來源工作表
                            OpenXmlSpreadsheetService.CopyWorksheetByName(
                                doc, workbookPart,
                                sourceSheetName: "工作表1",
                                newSheetName: dd.Day.ToString());

                            dd = dd.AddDays(1);
                        }

                        //儲存
                        workbookPart.Workbook.Save();
                    }
                }
                
                using (var workbook = new XLWorkbook(memoryStream))
                {
                    /*後續資料處理*/
                }
}

private void CopyWorksheetByName(
            SpreadsheetDocument doc, WorkbookPart workbookPart,
            string sourceSheetName, string newSheetName)
        {
            //取得要複製的來源工作表
            WorksheetPart sourceSheetPart = (WorksheetPart)workbookPart.GetPartById(
                workbookPart.Workbook.Descendants<Sheet>()
                .Where(s => s.Name.Value.Equals(sourceSheetName))
                .First()
                .Id);

            //利用 AddPart 來進行複製
            SpreadsheetDocument tempSheet = SpreadsheetDocument.Create(new MemoryStream(), doc.DocumentType);
            WorkbookPart tempWorkbookPart = tempSheet.AddWorkbookPart();
            WorksheetPart tempWorksheetPart = tempWorkbookPart.AddPart<WorksheetPart>(sourceSheetPart);

            //新增 sheet 並與工作表進行關聯
            WorksheetPart clonedSheet = workbookPart.AddPart<WorksheetPart>(tempWorksheetPart);

            //新增新的工作表到主要的活頁簿中
            Sheets sheets = workbookPart.Workbook.GetFirstChild<Sheets>();
            Sheet copiedSheet = new Sheet()
            {
                Name = newSheetName,
                Id = workbookPart.GetIdOfPart(clonedSheet),
                SheetId = (uint)sheets.ChildElements.Count + 1,
            };

            sheets.Append(copiedSheet);
        }

參考：

• https://stackoverflow.com/questions/50856596/c-sharp-openxml-copy-and-paste-excel-sheet-to-new-workbook
• https://stackoverflow.com/questions/58733258/openxml-how-to-copy-a-worksheet-to-another-workbook

如果需要改到圖表的公式：https://social.msdn.microsoft.com/Forums/en-US/cc811704-411d-43e9-8b11-3901571aaf9d/open-xml-excel-charts?forum=oxmlsdk