I don't think the document you linked to is trying to say you can convert from Excel back to TDMS. What is is saying is that Diadem, and the DataFinder toolkit, have plugins for loading data, indexing it, and searching. TDMS and Excel files can both be imported and indexed and I read the document as suggesting to convert the TDMS into an Excel file (of which there are a few examples online), then edit the Excel file, then let the file importer use the modified file.
Editing a TDMS file is difficult for a few reasons. If you are just deleting samples from channels, then NI does provide a way to do that in LabVIEW. If you are trying to edit values, then the only solution I know if is to read from one file, and write to a new one, editing the data you want, and then delete the original file.