Grace is irresistible in regeneration or the new birth, Jesus says Jn 3:7-8
7 Marvel not that I said unto thee, Ye must be born again.
8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.
This is saying how the new birth takes place ie spiritually rather than re-entering a womb to be physically born again, not an intention to say nicodemos couldn't libertarianly decide where to undergo it.