you cant
you need a metal coat
catch magnemites
give the metal coat to sciceor and then trade
Simply trade a scyther from firered while it holds metal coat to emerald you will receive a Scizor.
catch scyther in fr lg or in emerald safari post e4 and give metal coat and trade
get an onix, then give it the item metal coat, and trade it to another game. it should evolve
Trade from fire red or leaf green. On fire red and leaf green its found on memorial pillar (in the sevii islands).
A Metal Coat can be found in New Mauville. The Metal Coat is on the right of the machine.
You can find it on a wild Magnemite or Magneton, but the chances are very slim at 5%. (1 in every wild 20 wild Magnemite or Magneton)
A metal coat makes an Onix evolve into a Steelix.
Trade Syther equipped with a metal coat to another game and then trade back. You get the metal coat on S.S. Aqua after defeating the elite 4.