Reply To: GREP – Greek characters

Have a look at https://creativepro.com/search-for-foreign-language-characters-in-text.php
where it mentions searching for Unicode ranges (scroll down a bit).
It seems 0370–03FF is the range you need to cover Greek.

May be worth checking if the authors
a. used proper Greek characters from that range
or
b. used the Symbol font, which can sometimes be a pain, as some versions of Symbol reuse the Latin range for Greek symbols for maths etc.

Good luck,
Chris.