First, scientists dug up some old bones. Fossils, actually — real direwolf teeth and skulls buried in the earth for 13,000 to 72,000 years. These bones still had tiny fragments of DNA inside — think of DNA as the instruction manual for building a creature. Of course, ancient DNA is like a book that’s been through a shredder and then set on fire, but with a lot of tech and patience, scientists can piece together a decent draft.
source https://timesofindia.indiatimes.com/science/direwolves-reborn-why-jon-snows-best-friend-isnt-really-back-from-extinction/articleshow/120099954.cms