ὄνομα δὲ ἐποιοῦντο οὐδενὶ αὐτῶν

I don’t understand how ἐποιοῦντο is being used here:
ἔθῡον πρότερον οἱ Πελασγοὶ τοῖς θεοῖς, ὄνομα δὲ ἐποιοῦντο οὐδενὶ αὐτῶν·

My book gives the translation: “Formerly the Pelasgians used to sacrifice to the gods but gave a name to none of them;”,
I can’t find any definition of “ποιοῦμαι” meaning “I give”. I was considering “a name was not made for any of them” but in that case the verb should be in the singular.

Can anyone please explain?

Betts, Gavin; Henry, Alan. Complete Ancient Greek: A Comprehensive Guide to Reading and Understanding Ancient Greek, with Original Texts (Complete Language Courses) (p. 267). John Murray Press. Kindle Edition.

Don’t be misled by English. Greek would not normally speak of “giving” a name, as if it were a gift (διδόναι, δῶρον). ποιεῖν, or middle ποιεῖσθαι, as in making, creating, producing, is a much better term, more idiomatic and more accurate. τίθεσθαι (ἐτίθεντο) would be another possibility. Both verbs have wide application.

Thanks but I still don’'t understand why the middle plural is used. Does it mean “they did not make in their own interest a name for any of them”?

The middle voice is sometimes more a matter of nuance than anything else. It always signals the engagement of the subject in some way but not necessarily “in their own interest.”