>>95994356
It's not on The Silmarillion because Christopher (mistakenly) made an effort to remove any mentions of Dagor Dagorath, although a coupl of mention of the "Last Battle" still remain.
Versions of the Last Battle can be found throughout the History of Middle-Earth volumes, in bit and pieces, though the wiki page actually shows Tollers' last version of it.
www.tolkiengateway.net/wiki/Dagor_Dagorath#The_Later_Quenta_Silmarillion