To evolve Eevee into Glaceon in Pokemon Go, you need to rename your Eevee as "Rea". After renaming your Eevee, you should quit and reload the app to double-check that the name change has taken place. Its worth noting that the nickname trick only works once per evolution, so make sure you choose carefully. Alternatively, you can use a Glacial Lure Module, which can be purchased from the in-game store for 200 coins, to evolve Eevee into Glaceon.