"Spell Check" feature: How can I delete a previously added personal new word?

Accidentally I added a new word “by mistake” (!), so that I would like to delete it again now.
I know already where the path to all eM Client files are…but when I click at the Spell Check language concerned (in my case it’s “en-AU.custdic”) I cannot open it, because it’s of course an unknown file extension (custdic). Since such editing feature does exist at various MS mail programs, I trust that this is also possible at eM Client…or??

just open it in e.g. Notepad and delete the row with the mistaken word, then restart eM Client and the spellcheck will work as you want it to.

Oh, “oops”!!
Indeed, this reply of yours should have been also for me “quite obvious” to start
with; he, he! So thank you for “refreshing” now my brain cells, dear Gabriel…