Converting uploaded excel file into CSV

Question

How do I covert Excel to CSV

I have the code below

 static void CovertExcelToCsv(string excelFilePath, string csvOutputFile, int worksheetNumber = 1)
        {
            if (!System.IO.File.Exists(excelFilePath)) throw new FileNotFoundException(excelFilePath);
            if (System.IO.File.Exists(csvOutputFile)) throw new ArgumentException("File exists: " + csvOutputFile);
            
            // connection string
            var cnnStr = String.Format("Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties=\"Excel 8.0;IMEX=1;HDR=NO\"", excelFilePath);
            var cnn = new System.Data.OleDb.OleDbConnection(cnnStr);

            // get schema, then data
            var dt = new DataTable();
            try
            {
                cnn.Open();
                var schemaTable = cnn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
                if (schemaTable.Rows.Count < worksheetNumber) throw new ArgumentException("The worksheet number provided cannot be found in the spreadsheet");
                string worksheet = schemaTable.Rows[worksheetNumber - 1]["table_name"].ToString().Replace("'", "");
                string sql = String.Format("select * from [{0}]", worksheet);
                var da = new OleDbDataAdapter(sql, cnn);
                da.Fill(dt);
            }
            catch (Exception e)
            {
                // ???
                throw e;
            }
            finally
            {
                // free resources
                cnn.Close();
            }

            // write out CSV data
            using (var wtr = new StreamWriter(csvOutputFile))
            {
                foreach (DataRow row in dt.Rows)
                {
                    bool firstLine = true;
                    foreach (DataColumn col in dt.Columns)
                    {
                        if (!firstLine) { wtr.Write(","); } else { firstLine = false; }
                        var data = row[col.ColumnName].ToString().Replace("\"", "\"\"");
                        wtr.Write(String.Format("\"{0}\"", data));
                    }
                    wtr.WriteLine();
                }
            }
        }

I already have a button that selects the folder to be coverted.

I would want to covert excel file from a folder in the project to csv and store the csv file in another folder. How would I define the path in this code.