A Secret Shared is an Errand in Horizon Zero Dawn: The Frozen Wilds DLC. This walkthrough shows how to complete the quest.
Recommended Level: 30
Location: North of Song’s Edge
Requirement: having finished Into the Frozen Wilds
Quest-Giver: Kamut
Reward: 5.000 XP, 1 Bluegleam, 1 Spear Modification Box
Trophy: 
First Spear Modification
Objectives:
- Find Rail Part
- Leave the Drone Hangar
- Talk to Kamut
This errand can be accepted just a few minutes into the game – after finishing the first side quest. Talk to the Shaman Kamut just a little to the north of Song’s Edge. He notices our spear and tells us where to find upgrade parts for it. For this, we have to travel up north quite a bit (or use fast-travel, if you’ve been there before) and rappel down into the Drone Hangar.
Inside the Hangar, Aloy has to solve two short puzzles in order to reach the desired part. You will see a ladder on the ride side – climb up to reach some other yellow climbing points on the ceiling which were inaccessible before. With those, you will reach another platform, where you can activate a console to move the drone to the right side.
The drone can now be used to climb up and proceed. To the right of the drone is a platform with a Banuk Figurine – grab it, while you’re already here. To continue our errand, we have to use the drone to jump in the other direction, though and we will see another one of the Halo-door-puzzles. Use your focus 
to see the correct solution (right / down / right).
Now, we have to navigate through some narrow shafts and will eventually reach the other drone in this hangar. The part we are looking for is located on it’s front-left side.
Once we have obtained it, we can now climb the dividing wall and head out of the hangar. Our journey will be briefly interrupted by a Demonic Stalker, but he can be dealt with quite easily. Climb out of the Hangar on the right side and use fast-travel to get back to the settlement nice and fast.
Head back to Kamut and talk to him. He will give us a Spear Modification Box, which we have to open from the Inventory (under Treasure Boxes). Once you have obtained the Mod, head over to the Crafting tab and upgrade your spear like any other weapon (just that spear Mod’s are unique and can’t be used on weapons – and weapon Mod’s can’t be used on the spear.)
This will net us the First Spear Modification-trophy and conclude this errand.
When you are entering the hangar, there are proximity alarms that go off. As you are exiting the hangar, you get attacked by a Stalker.