This page of the Assassin's Creed Valhalla guide will walk you through the steps towards successfully completing the main storyline of the game.
At the end of Assassin's Creed Valhalla's main storyline, we see Eivor and Sigurd return to the Hordafylke region in Norway to say goodbye to their father, Styrbjorn.
Sigurd finally realizes that his visions were actually the memories of Tyr, one of the Norse gods, and leads Eivor to the temple of Goinnhellir (Yggdrasil Chamber). The characters reach the simulation device and use it to enter Valhalla.
After spending a few days in Valhalla, Eivor realizes that they are stuck in a simulation and are being fed all sorts of lies. Eivor decides leave this place, after convincing Sigurd to come along. When they manage to get out of the trap, Basim (the reincarnation of Loki, another Norse God) stands in their way.
At this stage of the game, Basim admits that all along he was seeking revenge for the misdeeds committed against his child (Fenrir) and joined Sigurd, thinking that he was Odin's reincarnation. It is at this moment that he realizes that Eivor was the one he was looking for. Eivor defeats Basim in the ensuing battle and, with Sigurd's help, locks him in the simulation for over 1,000 years.
During the conversation with their brother, Eivor will mention returning home, and Siegfried will give his honest opinion about Eivor and the winding paths of their friendship. It is at this point that Eivor will become the new Jarl of the Raven Clan, and Sigurd may (or may not - depending on your choices) decide to return to England with Eivor.
Upon returning to Ravensthorpe, you'll get a cutscene of Siegfried making good on his promise to his sibling and appoints them the new Jarl of the Raven Clan. All the settlement's residents greet their new Jarl with delight.