Before registering for the Island Challenge, the Kahuna of Melemele Island will inform you about Captain Ilima and the Trial at Iki Town Memorial Hill. He will tell you to come back after catching a Pokémon and reaching Level 7.

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You can check your Pokémon’s level by pressing the “Y” button and selecting “Pokémon.” Once your Pokémon reaches Level 7, return to Captain Ilima at Iki Town Memorial Hill to participate in the Trial. Passing the Trial will earn you the Normalium Z and progress you further in the game.