How do you get the Eternal Reign Icon?
It was a mission or event reward. Riot's description in the client reads: “Earned by participating in the 2018 VS. event to celebrate Garen's victory over Darius.”
Is the Eternal Reign Icon still available?
No. Riot tied the Eternal Reign Icon to 2018 (mission reward), and it does not normally bring back past event rewards or bundles.
