This page of the Assassin's Creed: Valhalla game guide includes a detailed walkthrough description of A New England side quest.
Award for completion: 1200 XP.
In the place marked in the picture above you will meet Hysing. The old man is clearly worried about something and does not seem to be fully healthy. At some point, Hysing wants to show Eivor the most important places in New England. Follow him and listen to what he has to say.
During the tour around the island, Hysing will make a few more stops and each time he will talk about another important place. Eventually, he will panic about finding his king and lead you to the camp.
The aforementioned king will be the straw dummy you have to approach and look at in order to move on to the next stage of this quest. Hysing has some real mental problems.
When you talk to him you can lie to make him happy. The old man will believe your words and leave the camp very pleased. If you choose the brutal truth, Hysing will start to speak about his king in a less flattering manner. The choice you make during the conversation does not affect the reward you receive for completing this quest.