To start The Never Ending Lecture side quest in The Legend of Zelda: Tears of the Kingdom, speak with Khira and Chroma in the throne room at Zora’s Domain. For this quest, you’ll need to travel to Ihen-a Shrine which can be found near Mipha Court at the top of Ploymus Mountain.
Once there, glide into a waterfall then use your Zora Armor to swim to the top where you’ll reach the Floating Scales Island.
Once on top of the fish-shaped sky island, head to the tail and on the east side look over the edge to find a cave.
Glide to it and go inside to find the chest containing the Zora Helm! After looting the chest, the quest will complete.