How do you get the Fiery Field dungeon in Pokemon Mystery Dungeon?

You can't actually get the Fiery Field dungeon in Pokemon Mystery Dungeon!

The Fiery Field is a location from the Pokemon games, not a dungeon in any of the Pokemon Mystery Dungeon titles.

Are you perhaps thinking of a different dungeon? Let me know the name of the dungeon or the Pokemon Mystery Dungeon game you're playing, and I can help you find information about it!