When you the enter Shrine Oman Au, look for a pedestal on the left side of the room. Place the Sheikah Slate on the pedestal to receive Magnesis. Magnesis allows you to pick up metallic objects and move them around.
Beginning the Magnesis Trial
When you pass the wall of stones, you will encounter a Small Guardian. You can quickly defeat it using a melee weapon.
2.2Monk Oman Au
With the Small Guardian out of the way, continue forward across a makeshift bridge made from a metallic plate. When you have crossed over, the path forward is blocked by a large pit. Activate Magnesis and move the metallic plate to create a new bridge forward.
There is a hidden metallic treasure chest on a high ledge to the left of the area before the metallic door. Use Magnesis to carry the treasure chest down to the ground. There is a Traveler’s Bow inside.
Continue forward to reach a large metallic door. Once again, activate Magnesis. This time, the object is attached on one side. You just need to swing the doors open to clear a path forward.
“May the goddess forever smile upon you.”
In the next room, you will meet the Monk Oman Au. Oman Au will give you a Spirit Orb, which is the treasure that the Old Man sent you inside to obtain.
With the Spirit Orb in hand, you will teleport out of the Shrine. In your next meeting with the Old Man, you will be tasked with retrieving additional Spirit Orbs from other Shrines located on the Great Plateau.