Hello! It's pretty simple. Open the game you want to edit and look for the header of the place you want to edit. The "Internal Name" can guide you, but the best way is to look for the header value in the map matrix editor. You will see Johto and Kanto and the header for each map. When you're in that header, in the header editor, look for the value in the "Wild Pokémon" column. That's the file index for the Wild Pokémon Editor.