Is it true that there's an eraser for the Death Note that can bring people back to life?
The Death Eraser appeared exclusively in the Death Note Pilot chapter, which isn't canon.

If the pilot chapter was considered canon several things would contradict themselves, like how the Rules of the Death Note contain that there are infinite number of pages in the Death Note, while in the pilot version it is stated that it has 60 pages with 38 lines per page.