In "Fishing Sail", players will receive the task of delivering the ring in Chapter 3.
The ring is located in Stellar Bay. Generally speaking, you need to complete the "Research Assistant" branch line. After obtaining the destroyer, install the destroyer on the motor of the research station, start the motor to interfere with the movement of the sea monster, and then fish with peace of mind.
But if you're quick enough, you can try to fish the ring out before it's destroyed.