A Workflow Manager local file must contain the correct suffix (for example CBL, JCL) in order for it to be opened with the required editor.
By default, the Endevor Attachment gets the dataset format information from Endevor. This information is passed to the Exit TAUENXA2 where you can adapt specific values if necessary.
If, for example, the file extension is not maintained in Endevor, you should use TAUENXA2 to associate the correct file suffix. To do this, locate the label set_defaults in TAUENXA2 and adapt the file extension variable o_fileext to your needs depending on the input parameter i_type, which contains the value of the Endevor element type.