Every now and then, you can receive special in-game gifts from Nintendo/The Pokémon Company. To find out if a gift is available, you can try checking the official websites, or the news channel via your Nintendo Switch. To receive a gift, go to “Communicate” from the main menu, then “Mystery Gift” on the left.
If successful, you’ll be given the following choices:
Get via Internet: Choose this to search for a gift that’s available to everyone via the Internet.
Get with code/password: If you’ve got a unique serial code or a common password, use this to input it and receive your gift.
Get with a Poké Ball Plus: Select this to receive your bonus Mew from your Poké Ball Plus. This can only be done once per Poké Ball Plus.
Check Mystery Gifts: Look up Mystery Gifts you’ve already obtained.