How To Get Mew & Jirachi - Pokémon (BDSP)

First you need to go to Florama Town.

Click Town Map option.

Have a chat with an old couple to the left.

Get Jirachi from the old man if you have saved data from SWORD/SHIELD.

Select YES! if you want to give a nickname to Jirachi.

Choose the "Add to your party " option when asked where to send Jirachi?

You need to select a Pokémon to swap from your party.

Jirachi will be added to your party and swapped one will be sent to a box.

The Old Man will wish you the grandest of adventures with this Pokémon.

The Old Lady will give you Mew if you have saved data from any of the Let's Go Games.

Mew will be added to your party!