On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough of The Body side quest .
Reward for completing the mission: 1200 XP.
In the place marked in the image picture, you will meet two children leaning over the body of a Viking warrior. When Eivor asks where his axe is, the children reply that a boy named Hurrey took it.
You will find the boy in the forest, not far from where you found the Viking's body. The boy will play a warrior and say that if you want the axe, you have to take it from him yourself. If you have level 4 Charisma, you can immediately convince the boy to give you the axe. Otherwise, you have to threaten him with a fistfight, and the boy will immediately give up and hand over the item.
After you manage to retrieve the axe, return to the Viking's body and ensure that he receives his weapon and can enter Valhalla.