There are a number of commercial editors for EDIFACT messages. A free editor is also sufficient.

Notepad++ has proved its worth. This makes it easy to insert a line break after the segment separator to make the file easier to read.

In this case, it is preferable to record a macro inside Notepad++ that performs the search and replace of the quotation mark with quotation mark and line-switching to keyboard shortcuts.

In the FAQ How to highlight EDIFACT segments? in color is also mentioned how to highlight EDIFACT segments in color.