Pokémon Sword and Shield’s The Crown Tundra expansion does a lot of new things, but it also has several elements that carry over from the base games and the Isle of Armor expansion as well.
One of the biggest similarities is in how you evolve a Galarian Slowpoke into the newly released Galarian Slowking.
In the Isle of Armor, players needed to gather a handful of Galarica Twigs and have a specific NPC weave them together into a Galarica Cuff. Once given to the Galarian Slowpoke, it’d evolve into a Galarian Slowbro.
In The Crown Tundra, you need to do something similar by collecting 15 Galarica Twigs and heading over to one of the smaller entrances of the Roaring-Sea Caves. Inside a specific entrance nestled to the left of the Frigid Sea, an NPC will offer to weave those twigs together into a Galarica Wreath.
That Galarica Wreath can then be given to your Galarian Slowpoke to evolve it into a Galarian Slowking. Once it evolves, you can instantly teach it its signature move, Eerie Spell.
To find Galarica Twigs, all you need to do is traverse either the Isle of Armor or Crown Tundra and interact with the sparkling item spots spread around the map. Some of these will end up being the twigs you need and you can use them to get either the Galarica Cuff or Galarica Wreath.