On this page of the Assassin's Creed Valhalla guide you will find a detailed walkthrough for Bewitched side quest.
Rewards: 1,200 XP.
In the place shown in the image above, you will find a locked hut. There is a boy trapped inside, crying out for help.
Go to the back of the hut and stand in the place shown in the image above. Aim through the window to break the lock on the front door.
Next, stand at the spot shown in the image above and smash the lock of the next door.
Now you can go inside. Go to the room on the left, push back the heavy bookcase and collect the key.
Return to the main chamber and open the door on the right. Inside you will find a boy complaining about being kidnapped by a witch. As it turns out later, this was a big lie.