For many people, filling up their Pokédex is one of the best feelings in gaming, and players of Sword and Shield are no different. The Isle of Armor DLC has introduced all manner of new Pokémon for you to track down in the game, and if you want to fill up the Dex, you will need to find all of them, and discover all their evolutions.
This makes an item like the Dragon Scale highly sought after, as you will need it to evolve Seadra into Kingdra. The Dragon Scale cannot be bought and is instead found in the Honeycalm Seas to the north of the Isle of Armor. If you head for the Training Lowlands, go to the shore and then use your Rotom Bike to cross the sea, you will get there easily.
You can find the Dragon Scale on a small sandbank in this area. It will appear as a Pokéball that you can pick up. To use the Dragon Scale, open your bag and go to the Other Items menu, then give it to Seadra. They will need to be holding the item when they are traded to another player to evolve into Kingdra, and the Dragon Scale will be consumed by this process.
Whomever you trade the Pokémon with will need to then trade it back to you, or trade you a Seadra that is also holding the Dragon Scale for you to get your Kingdra.