In Assassin's Creed Valhalla you can encounter Rigsogur Fragments. These are collectibles obtainable 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 max out the Grantebridgescire region.
The second page of the saga can be found in Grantebridge.
First, you must enter the church. It's best to do it by entering the cave just below the building.
Inside, you will see a glowing document, all you have to do is to run to it, and it will go into your inventory.