This page of the Assassin's Creed Valhalla guide has a detailed walkthrough of The Cult of Saint Guthlac side quest.
Rewards: 1,200 XP.
Go to the place marked in the picture above – you will meet a monk. The man was transporting apples, but his cart was destroyed.
The apples were to be delivered to a nearby farm. Pick up the crate lying on the road and follow the monk.
When you reach the destination, all you have to do is place the crate near the monk – the mission will be completed automatically.