On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough for Freya's Friend side quest.
Rewards: 1,200 XP.
In the place marked in the picture above, you will encounter a white cat. When you activate the quest, the cat will start running away – your task is to catch it.
The cat will stop in the place shown in the picture above. Pet it and the owner will appear. Talk to him to complete this task.
If the cat gets stuck on something, just throw torches at it to make the animal move again and reach the place indicated in the picture above.