On this page of our guide for Assassin's Creed Valhalla you will find a detailed walkthrough for the mission titled Childhood Sweetheart.
Birstan and Estrid are planning to part, but their parting will not be easy because of their political ties. Eivor must find Alfida and bring her to Birstan. The man hopes that after 20 years of separation they can still be together.
Rewards: 3400 XP.
Find and speak to Alfida
As far as we know, the woman is in Maeldun and you should find her in the last house on the cliff. Unfortunately, the building is completely empty and there are guards around.
Investigate the bonfire and you will find out, someone interrupted preparing the supper. It is possible that the household members were kidnapped.
The second bed shows that Alfida does not live alone.
Go outside and examine the last trace - a bucket and spilled water. Apparently someone was in a great hurry.
Behind the crates, in a makeshift cell, Eluric, Alfida's brother, is hiding. The man will tell you that his sister was taken away by Aelfred's men for standing up for a child. The woman is now in prison in Brentwood.
Find and rescue Alfida
The prison Eluric talked about is a long way from Maeldun - at the other end of Essexe.
Brentwood is very well protected and the prison is located in the middle of the settlement. If you want to act quietly, enter the camp through one of the alternative entrances - a hole under the palisade in the back of the camp.
You will get straight to your destination through the channel. The building where Alfida is being held is guarded and locked. The key is in the possession of one of the elite leaders.
If you want to eliminate him quietly, sneak to the observation towers, eliminate weaker enemies, and then attack the leader from above.
Enter the building and take Alfida on your back (she can't go by herself because she sprained her ankle) and then take her outside the camp.
Call a horse and take Alfida to a secluded lake house in the Epinga forest to meet her brother.
Put the woman on a bed inside the house to activate the cut-scene and talk to Alphida. When you tell her why you came, the woman will say that she will give Birstan a chance. The mission will end, and you will receive 3400 XP as a reward.