This page explains how to start and complete the The Undefeated Champ shrine quest.
How to Start the Quest
Before you can challenge this shrine, you have to reach Gerudo Town and free Divine Beast Vah Nabooris. After that, talk to Tali at the Sand-Seal Rally south of Gerudo Town to start the quest.
How to Complete the Quest
Check the Raqa Zunzo Shrine page for details on completing the quest.