How do elves re-embody?

Durelen:

HoME10 is 'Morgoth's Ring'; on 'of re-birth and other dooms of those that go to manaos'

Now the Eldar hold that to each elf-child a new fea is given, not akin to the fear of the parents....;and this fea either did not exist before birth, or is the fea of one that is re-born.