Trainers who purchase either the Pokémon Sword Expansion Pass or the Pokémon Shield 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 in-game bonus. Players will be able to receive these items after the release of The Isle of Armor (by the end of June 2020) until 7:59 a.m. PDT on Monday, August 31, 2020. 
 To receive the above items, you’ll need to open the X menu. From the X menu in your game, go to Mystery Gift, select Get a Mystery Gift, then select Get via Internet. 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.) You can see the clothing items you’ve received by visiting an in-game boutique fitting room.
 An internet connection is required to receive the above items.
 A paid Nintendo Switch Online membership is not required to receive the above items.
 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.
Source: The Pokémon Company International