Set Eevee as your Buddy Pokémon and earn 70 hearts with it
Make sure Eevee knows a Fairy-type move if required by the current game conditions
Have enough Eevee Candy
Tap Evolve when the Sylveon silhouette appears on Eevee’s evolution button
Use the nickname trick only once per account by renaming Eevee to Kira before evolving, if available and unused