On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough for The Twit Saga, part 2 side quest.
Rewards: 1,200 XP.
In the place marked on the above picture you will find a camp guarded by several mercenaries - deal with them to proceed to the next stage of this quest.
Free a viking soldier you may remember from a side mission in Ledecestrescire. The man will tell you the story of how he got into trouble and then places all the blame on his brother, who is currently unconscious.
Pick up the unconscious man, then follow the viking. Once you are a safe distance away, place the man on the ground.
After a while you will be attacked by a squad of Anglo-Saxon warriors. Defeat all opponents and speak with the viking to complete this quest.