After you're turned away at the Gerudo Palace, Dohna suggests you repair smaller rifts to prove yourself. One is south of the oasis.

Where to Start the Quest

You can start the quest during A Rift in the Gerudo Desert after you visit Chief Seera in the palace in Gerudo Town. Leave the palace to get a message from Dohna, then talk to Dohna in the Oasis. Then go to the southern location marked on the map and approach the soldiers to see a cutscene. This starts the quest.

How to Complete the Quest

Defeat the two dark monsters that pop out of the rift.