Where in icefall cave can you capture a delibird Pokemon FireRed?

You can't catch a Delibird in Icefall Cave in Pokémon FireRed. Delibird is a Generation II Pokémon and is not available in FireRed.

FireRed only includes Pokémon from the original 151 in the Kanto region.

If you want to catch a Delibird, you'll need to play Pokémon Gold, Silver, or Crystal.