Those that purchase the Expansion Pass for Pokémon Sword and Shield can get a couple of different outfits for their in-game avatar.

Early-purchase bonus!

Players who purchase the Expansion Pass soon after the launch of The Isle of Armor expansion (or players who have already prepurchased it) will be able to receive Leon’s cap and tights as an early-purchase bonus.

Players will be able to receive these items after the release of The Isle of Armor (June 2020) until 7:59 a.m. PDT on Monday, August 31.

Availability period: From the release of The Isle of Armor until 7:59 a.m. PDT on Monday, August 31. To receive the items after the release of The Isle of Armor:

1. Open the X menu in your game.
2. Select Mystery Gift.
3. Select Get a Mystery Gift.
4. Select Get via Internet*

Remember that you can change your clothes in the fitting room of any boutique.

The Mystery Gift menu option will appear in the X menu after you visit your first Pokémon Center in Pokémon Sword and Pokémon Shield. (This occurs after about an hour of gameplay. However, individual gameplay time may vary.)

An internet connection is required to receive the above items.
A Nintendo Switch Online membership (paid) is not required to receive the above items.
You can see the clothing items you’ve received by visiting a boutique fitting room.
Those who purchased the Expansion Pass before the above items were revealed will still be able to receive these items after the release of The Isle of Armor.

Special purchase bonus

If you purchase the Expansion Pass, you’ll be able to receive a Pikachu Uniform and an Eevee Uniform as a special purchase bonus. You’ll be able to wear these outfits in the expansions, of course, but also in Pokémon Sword and Pokémon Shield! Until The Isle of Armor’s release, it might not be a bad idea to complete your adventures in the Galar region decked out in your new outfit!

Use these steps, along with your code, to receive a Pikachu Uniform and an Eevee Uniform.

1. Launch your Pokémon Sword or Pokémon Shield game.
2. Select Mystery Gift on the X menu.
3. Select Get a Mystery Gift.
4. Select Get with Code/Password to connect to the internet.*
5. Enter your code.
6. Watch as the gift arrives in your game.
7. Be sure to save your game.

*Wireless broadband internet access required for online features. For more information, go to support.nintendo.com. See participating retailers for details. Server maintenance is scheduled to take place throughout the year. Code redemptions will not be possible during these times. Visit Pokemon.com for more information. One code per person; this code is not for resale. Games and system sold separately. Content distribution may be offered via online services at a future date. Gifts may become unavailable after a certain amount of time has passed since the release of Pokémon Sword and Pokémon Shield.

Upon purchase of the Expansion Pass, an email with your codes will be sent to the email address registered to your Nintendo Account. From the in-game menu, go to Mystery Gift, select Get with Code/Password, and then enter your codes.

If you didn’t receive the email, or if you accidentally deleted it, please log in to the Nintendo Account with which you purchased the Expansion Pass using a personal computer or smart device. You will be able to check the codes in the usage records found in the shop menu.

The Mystery Gift menu option will appear in your game after you visit your first Pokémon Center. (This occurs after about one hour of gameplay, though individual gameplay time may vary.)

A Nintendo Switch Online membership (paid) is not required.

You will get one code for the Pikachu Uniform and one code for the Eevee Uniform. Each can only be redeemed in a single save file. You won’t be able to use these codes to claim the same outfit in multiple save files.

Source: https://swordshield.pokemon.com/en-us/expansionpass/bonus/

YouTube Clip - Pokémon Sword and Shield NEWS #10

Source: https://www.youtube.com/watch?v=Ff9tcIbMMtU