Once you have unlocked the Season Pass content, this quest will be available as soon as you reach England. To begin, you’ll need to find and speak with Bjorn, the mysterious berserker. You’ll find him in the region of East Anglia, in a cave south of the town of Northwic.
Speak with Bjorn in East Anglia
As you approach the cave Eivor will note the presence of Bjorn nearby. If you’re having trouble locating the cave, use your raven to scout the area. The entrance to the cave is enormous, so it will be difficult to miss. Speak with Bjorn in the cave and listen to what he has to say. He’ll ask you to prove yourself by hunting with his white bear, Njal, and if the bear trusts Eivor he may consider the offer of help.
Follow Njal the Bear and Fish for Bullheads
Follow the bear through the cave to the other side, then south along the river. When you reach the shore, you’ll need to fish for some Bullhead to feed Njal. There are plenty in these waters, and you can use Odin’s Sight to highlight those nearby. This will be easier if you have the fishing line, but don’t worry if not; you can shoot the fish or slash at those in shallow waters with melee weapons. You should only need to kill and loot one fish, then speak with Njal.
Kill the Mercian Soldiers
Once Njall has eaten, you’ll be tasked with killing some Mercian soldiers. They will attack from the fields to the southeast, so be ready for them. Among the soldiers there will be two skirmishers, who can be tricky to hit if you don’t know how. They will evade most of your strikes, but if you dodge first and then strike with a light or heavy attack, it will almost always hit.
When the Mercian soldiers are dead, return to Bjorn outside the cave to the north and help him defeat the Mercian soldiers there. You’ll find a few archers, a couple of skirmishers, and a Goliath elite. The Goliath has weak points on their left hand and left leg. Shoot them as soon as possible to make them vulnerable to a stun attack, which will take a good chunk of health in one hit. Otherwise, you can just as easily bring the Goliath down with regular hits as Bjorn tanks them.
Once all the soldiers are dead, speak with Bjorn to begin a cutscene, after which the quest will complete.