Add specific rows to DataFrame C#

Question

I'm currently trying to read out an Excel file and add specif rows to a C# DataFrame. This is my current code:

public static string Do_forecast(string file_guid)
        {
            PrimitiveDataFrameColumn<int> tecId = new PrimitiveDataFrameColumn<int>("TecID");
            StringDataFrameColumn email = new StringDataFrameColumn("Email");
            StringDataFrameColumn art_nr = new StringDataFrameColumn("Art Nr");
            StringDataFrameColumn article_nr = new StringDataFrameColumn("Article Nr");
            StringDataFrameColumn brand = new StringDataFrameColumn("Brand");
            StringDataFrameColumn article_group = new StringDataFrameColumn("Article Group");
            PrimitiveDataFrameColumn<DateTime> date = new PrimitiveDataFrameColumn<DateTime>("Date");
            PrimitiveDataFrameColumn<DateTime> date_of_stock = new PrimitiveDataFrameColumn<DateTime>("Date of Stock");
            PrimitiveDataFrameColumn<float> sales_base_line = new PrimitiveDataFrameColumn<float>("Sales base line");
            PrimitiveDataFrameColumn<float> sales_upper_boundaries = new PrimitiveDataFrameColumn<float>("Sales upper boundaries");
            PrimitiveDataFrameColumn<float> sales_lower_boundaries = new PrimitiveDataFrameColumn<float>("Sales lower boundaries");
            PrimitiveDataFrameColumn<DateTime> simple_prediction_of_order_date = new PrimitiveDataFrameColumn<DateTime>("Simple Prediction of order date");
            PrimitiveDataFrameColumn<int> order_value = new PrimitiveDataFrameColumn<int>("Order Value");
            StringDataFrameColumn note = new StringDataFrameColumn("Note");
            PrimitiveDataFrameColumn<int> stock = new PrimitiveDataFrameColumn<int>("Stock");
            PrimitiveDataFrameColumn<int> stock_Limit_min = new PrimitiveDataFrameColumn<int>("Stock Limit min");
            PrimitiveDataFrameColumn<int> stock_Limit_max = new PrimitiveDataFrameColumn<int>("Stock Limit max");
            PrimitiveDataFrameColumn<int> open_Orders = new PrimitiveDataFrameColumn<int>("open Orders");
            PrimitiveDataFrameColumn<int> reservations = new PrimitiveDataFrameColumn<int>("Reservations");
            PrimitiveDataFrameColumn<int> delivery_days = new PrimitiveDataFrameColumn<int>("Estimated time in delivery days");
            PrimitiveDataFrameColumn<int> sales = new PrimitiveDataFrameColumn<int>("Sales");


            string tempFilePath = Path.GetTempPath();

            string infile = file_guid + ".xlsx";
            string outfile = file_guid + "_output.xlsx";
            string local_in_file_path = Path.Combine(tempFilePath, infile);
            string local_out_file_path = Path.Combine(tempFilePath, outfile);


            FileInfo existingFile = new FileInfo(local_in_file_path);
            using (ExcelPackage package = new ExcelPackage(existingFile))
            {
                ExcelWorksheet worksheet = package.Workbook.Worksheets[1];
                int colCount = worksheet.Dimension.End.Column;  //get Column Count
                int rowCount = worksheet.Dimension.End.Row;     //get row count
                List<string> articlelist = new List<string>();
         
                for (int row = 1; row <= rowCount; row++)
                {
                    if (articlelist.Contains(worksheet.Cells[row, 3].Value?.ToString().Trim()))
                    {
                        continue;
                    }
                    else
                    {
                        articlelist.Add(worksheet.Cells[row, 3].Value?.ToString().Trim());
                    }
                }

                for (int row = 1; row <= rowCount; row++)
                {
                    foreach (var article in articlelist)
                    {
                        Console.WriteLine(article);
                        if (row != 1 && worksheet.Cells[row, 3].Value?.ToString().Trim() == article)
                        {
                            
                            art_nr.Append(worksheet.Cells[row, 3].Value?.ToString().Trim());
                            date.Append(DateTime.Parse(worksheet.Cells[row, 4].Value?.ToString().Trim()));
                            sales.Append(Convert.ToInt32(worksheet.Cells[row, 5].Value));
                            brand.Append(worksheet.Cells[row, 6].Value?.ToString().Trim());
                            article_group.Append(worksheet.Cells[row, 7].Value?.ToString().Trim());
                            stock.Append(Convert.ToInt32(worksheet.Cells[row, 8].Value));
                            date_of_stock.Append(DateTime.Parse(worksheet.Cells[row, 9].Value?.ToString().Trim()));
                            reservations.Append(Convert.ToInt32(worksheet.Cells[row, 10].Value));
                            open_Orders.Append(Convert.ToInt32(worksheet.Cells[row, 11].Value));
                            stock_Limit_min.Append(Convert.ToInt32(worksheet.Cells[row, 12].Value));
                            stock_Limit_max.Append(Convert.ToInt32(worksheet.Cells[row, 13].Value));
                            delivery_days.Append(Convert.ToInt32(worksheet.Cells[row, 14].Value));
                            DataFrame df_to_forecast = new DataFrame(art_nr, date, sales, brand, article_group, stock, date_of_stock, reservations, open_Orders, stock_Limit_min, stock_Limit_max, delivery_days);
                            //DataFrame df_out = new DataFrame(tecId, email, article_nr, brand, date, sales_base_line, sales_upper_boundaries, sales_lower_boundaries, simple_prediction_of_order_date, order_value, note, stock, stock_Limit_min, stock_Limit_max, open_Orders, reservations);
                            Console.WriteLine(df_to_forecast);
                        }

                    }

                }
            }
            return file_guid;
        }

So I'm adding every unique article value from the 3rd Excel column to the articlelist. In the second foreach loop is now my problem: I try to add all rows just from one article to the DataFrame. In my current try all rows get added to the DataFrame, I can also understand why, so I know that it can't work like this. But I dont really know how I should do it different. How can I solve this problem?