There’s only one Cursed Area on the Isle of Skye, and it can only be found as part of the Tossing and Turning main quest.
How to Destroy the Cursed Symbol at the Cursed Church
When you arrive at the Cursed Church, a cutscene will play during which Eivor is introduced to Kassandra. After a brief exchange, they fight, until they both realise that there’s something more to the other. Once they’ve agreed to help each other in order to stop the nightmares and make the Isle of Skye safe again, the cutscene will end. At this point you’ll need to walk up the steps to the church, and force it open with Kassandra’s help in the same way that you do with your companions during raids. Once you’re inside you’ll see a barricaded entrance on the ground. You can use a fire pot (found outside the church) or the Incendiary Powder Trap ability to destroy it, then jump down.
In the room beneath the church you’ll find a movable barricade, behind which there’s some minor loot and a fire pot. You can use the fire pot to destroy the barricade on the wall in the main part of the room, or you can use Incendiary Powder Trap again. Either way, once the barricade has been destroyed you’ll be able to shoot the Cursed Symbol, thereby removing the curse from the area. With the symbol destroyed, head outside and go through the crack in the cave wall to find some more minor loot, before heading outside to confront some enemies. These will be easy to deal with, especially with Kassandra by your side. When all the enemies are dead another long cutscene will play out, during which you’ll have the opportunity to ask Kassandra some questions. At the end of the scene Kassandra will ask you to meet her in Tobhta, and the quest will end.