In Assassin's Creed Valhalla, you may come across Rigsogur Fragments, which are a type of collectibles in the game. On this page of the guide, you will learn where to find the collectible and how to reach it. This will make it easier for you to complete East Anglia in 100%.
The third page of the saga can be found in Northwic.
First, you have to enter the building and then move the shelf blocking the passage to the curtained room.
Inside, you will see a ladder. Before you jump on it, destroy the wooden ceiling at the top. This will let you get to the mezzanine, on middle floor, where you'll find many documents.
On the desk, to the left, there is another fragment that you can read.