In various unmarked Kett camps throughout Voeld you’ll find dead Angara. You’ll have to scan several of these deaders to advance the quest, and they appear randomly, so undertaking the painstaking labor of continuously clearing out candidate camps is the only way to complete this objective. After you scan enough bodies, you’ll get a navpoint directing you to a location southeast of Techiix Station.
Here you’ll find a cave. A heavily fortified cave. Crawling with Kett. The foes you’ll face include plenty of Chosen and Anointed, along the with the odd Wraith and Destined. Crush your opposition, turn around and occupy the positions they previously held and wait for Kett reinforcements to show up via dropship. After these Kett are destroyed, head into the cave to find a captive Angara. Activate a Console to free the Angara, then talk to said Angara - Maaravet - who will cautiously thank you for your rescue. Your valiant rescue is worth 530 XP.