A useful item for anyone looking to evolve their Feebas into a Milotic in Pokémon Sword and Shield is the Prism Scale. It’s a small item you need to give your Feebas and then trade that Pokémon with a friend to have it evolve into a Milotic. When it evolves, you can receive it again and add it to your collection.
To find the Prism Scale, you have a handful of options available to you. The first one is locating it on Route 2. However, you can’t do it early. You need to wait until you receive the Rotom Bicycle upgrade to travel across water. When you have it, go back to Route 2 and go to the Professor’s house and proceed to the west of the home. Go across the water to the island. When you’re there, go to the northwest, and you should see a distinct sparkle in the water near the other piece of land. Go to it, and pick up your first Prism Scale.
You have the chance to locate the Prism Scale in another location, the South Lake Miloch, inside of the Wild Area. You need to roam around the southern portion of the area, looking for similar glitters in the water. It’s not a guaranteed drop, but if you consistently check back in the area, you should find it after a handful of rotations.
After you acquire the item, you’re good to go, and you can freely trade your Feebas with a friend of yours who will trade it back to you. We do know where you need to go to find a Feebas, too.