How does 何で usage exactly work with 言う?


So I know that 何で can be used to ask 'why' or to ask "with what" in a
negatively structured sentence. Like, お姉ちゃんは何で学校に行きますか.

But when I wanted to learn how to say, "idk what to say" a Japanese person
suggested the same usage to me, like 何で言えばいいか分からない so i'm curious now why
isn't it 何を?

I'm a newbie learner sorry if this looks funny.




As other answers pointed out, it was

> 何て言えばいいか分からない

何て means "indefinite way" or "how" and it's the adverb form of 何.

It literally means: "If I say (it) in an indefinite way, I wouldn't understand
if it's good". -> "I don't know how to say it"

