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 complete Ledecestrescire region in 100%.
The first page of the saga can be found in the city of Repton.
First, you must enter the destroyed church. The easiest way to do it is through the roof. There is a big hole there. Your character will easily fit inside. Climb on top and jump immediately inside.
Inside you will see a passage to the basement/tunnels. Jump from the upper boards and go to the dungeons. There you will find a valuable treasure and a few more items you can collect.
The first page is located on a coffin, on the left side of the room. You can pick it up and immediately leave the room. The room won't be dangerous, but it won't offer any other valuable items as well.