To the northeast is a place called Keener’s Rock, printed on the map as a small hut with a campfire next to it. It’s not far from the Cut’s only Hunting Grounds. Make your way to this point however you can until you discover the Keener’s Rock gate. The green marker for the side quest should show up once you get close enough to the tiny settlement.
Seek out the Chieftain of the White Teeth werak and interact with him to learn of the trials currently taking place in the Hunting Grounds. The White Teeth are recruiting new hunters – they have to spend four days and four nights in the harsh cold of the mountains. Any that don’t return are left behind, but they’re not strictly allowed to help one another complete the challenge.
When the Chieftain explains that two of the hunters have not returned, and that the werak have no intention of going to look for them, Aloy takes it upon herself to find them instead.
Activate the quest from the menu and follow the waypoint; the trek isn’t too far, so you should be able to tackle it on foot rather quickly. You’ll eventually come to a zipwire with a herd of machines in the valley below. One of the missing trial-goers is killing the machines, so make your way down there and help her out – you’ll need to take out a few Watchers and some Lancehorns. When this is done it will initiate a cutscene, but Aloy and Ikrie’s conversation is cut short by the interruption of a Scrapper ambush.
During battle with the Scrappers, a pair of Glinthawks will join the fray, too. Make sure to kill all the machines, then return to Ikrie to find out why she hasn’t yet returned to Keener’s Rock. The other trial-goer, Mailen, is injured and refuses help, but Ikrie doesn’t want to leave her behind. When the conversation is over, follow Ikrie to Mailen’s location.
Upon arrival the place is surrounded by three Longleg machines, with Mailen sheltered and unseen for now. Begin taking them out only to be joined by Scrappers again. Once you’ve dropped all these machines, prepare to face a Scorcher.
Once the fight is finally over you can return to Ikrie and Mailen. It will activate a cutscene where Aloy tries to help, but Mailen is stubborn and honours the laws of the Banuk. Mailen makes her way back to Keener’s Rock, but Ikrie decides to stay lost.
Return to the White Teeth Chieftain to finish the quest.