This page explains how to start and complete the Frog Catching side quest.
How to Start the Quest
First, you need to complete the Divine Beast Vah Ruta Dungeon. Then you can talk to Tumbo, a Zora boy who runs around Mipha's statue during the day and can be found in the area beneath the throne room at night.
How to Complete the Quest
Give Tumbo five Hot-Footed Frogs. This type of frog can be found along the road southwest of Zora's Domain.
Quest Reward
Tumbo gives you an Armoranth.