Because in the official games, evolving Eevee is permanent. In this fan game, you can reverse evolution or choose which evolution to trigger via a "Harmony Meter."
If your search for a was simply looking for the classic trio from the original games, here is how you obtain them. Pokemon Evolve Eevee -Normal Download Link-
: Use a or Ice Stone , or level up near a Mossy Rock or Icy Rock in certain games. Because in the official games, evolving Eevee is permanent
github[dot]com / PokeEvoProject / Eevee-Evolution-Normal Because in the official games
maintains an updated list of the 'Name Trick' nicknames for Pokémon GO. Official Pokédex