Giles,

It sounds like you're trying to define something for two single apostrophes (read prime singularly, and prime prime in a pair). 

I would try a regex match on: 
''(.*)''    [That's apostrophe apostrophe left parenthesis dot asterisk right parenthesis apostrophe apostrophe]
with the replacement string being:
quote \1 quote

and see how that works.  Do it in the default dictionary, as this regex match is not likely at all to match anything but this odd case.  If it happens to catch something else, then we can work on figuring out how to limit what it catches further.  But the combination of two successive single quote marks is almost unheard of in typical written English.  (Let's not get in to mathematical notation here, and I doubt you're using that anyway.)

It's interesting, as I've never seen anything that does two apostrophes/single quote marks as a substitution for the much more common double quote mark.
--

Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042  

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