If you want to complete your Pokédex in Sword and Shield, you'll need to do more than hang around to catch The Pokémon. Some rare Pokémon can only be obtained through specific means, and some are hidden behind trades with NPCs. One of these Pokemon is Unova Tutafeh.
The first thing you will need to get Unova Tutafeh is a Gallery Tutafeh. You can find one on Route 6, so head there and you should be able to find one pretty quickly. Head to Baloonle Stadium and you'll find a trainer in an Even costume. Talk to them and they will offer you Unova Tutafeh in exchange for your Galarian Tutafeh.
When you get your Unova Tutafeh, add it to your party and level it to 38 to turn it into a Tutankafer. You don't have to do anything special or give her a particular item; it will just evolve automatically. She is the only Unova Tutafeh in the game; you can't get more through breeding. All eggs from an Unova Tutafeh will yield a Gallery Tutafeh. When you add this hard-to-find Pokemon to your Pokédex, you'll be one step closer to completing it.
If you need more help with Pokémon Sword and Shield, we've got a whole range of guides you might find useful. Learn how to use PC Box Link, change a Pokémon's nature, and trade The Pokémon. If you're looking for The rarest Pokemon, we can also tell you where to find Fantyrm and Ditto.