On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough description of the side quest The Demon Odour at the Tithe.
Rewards: 1,200 XP.
In the place marked in the above picture, you will meet a man trapped in a warehouse. To get to it you will have to overcome a small obstacle course.
The liquid in the jugs is flammable so do not use fire to avoid accidentally dying while rescuing the trapped man.
Once you enter the warehouse, destroy the jugs on the left, then move the bookcase aside to move on. Smash more jugs and move the second obstacle. Then repeat the same action with the next obstacle.
You will eventually reach the man who cried out for help. Follow him outside and talk to complete this task.