Catch an Eevee
Set Eevee as your buddy
Walk 10 km with Eevee as your buddy
Earn 2 Eevee candies while Eevee is your buddy
Evolve Eevee during the day near a Mossy Lure Module for Leafeon, or near a Glacial Lure Module for Glaceon
Make sure you are near a Glacial Lure Module when evolving Eevee to get Glaceon
Use the nickname trick once by renaming Eevee to Rea before evolving, if you have not used it already
Confirm the evolution preview shows Glaceon before evolving