Once On An Island, Look Under Your Minimap For The Camera Button.
- This Opens Selfie Mode.
Press (Print Screen) On Your Keyboard, While In Selfie Mode, To Gain Progress For This Achievement.
Unfortunately, Lagoon Island Is An "Adventure Island". These Only Spawn 5 Times A Day For 2-4 Minutes Each Spawn Time.
- Also They Do Not Spawn Everyday.
You Can Check Spawn Timers In Game With The Compass Below The Minimap.
- You Can Check What Days They Spawn, In Advance, Here:
https://lostarkcodex.com/us/eventcalendar/----------------------------------
Achievement Is Tracked In-Game (Achievements Tab) And Pops Immediately After The Last Island.
Good Luck!