you cant.you have to get it in an event.then go to ilex forest,and you see your rival's past.
You Can Not Catch Celabi In Pokemon Firered Unless you trade with pokemon heartgold or soulsilver.
you can't
you get it by an event.
You can only find celebi in the special event.
Sorry its only a wifi event and im pretty sure it passed...
Mystery Gift.
You have to migrate a Pokemon to Pal Park.
You cannot catch Celebi unless you are using cheat codes or waiting for Pokemon events.
You cannot CATCH Celebi on Pokemon HeartGold or SoulSilver, but there is an wifi event a Gamestop that gives you a Celebi in mystery gift. You can also use a Action Replay™, but I suggest you do the event.
You cant it was a speacial event
you can not get him in the game
you cant