This is a Wild Area event held by Sword and Shield. With this event, you get a chance to encounter Giganantamax Meowth; and with 5-stars raids, you get a chance to land on a 2% guaranteed Shiny Galar Meowth slot. You also get to encounter the various different forms of Meowth.
To import these files into your save, use PKHeX's block importing function. Our tutorial should guide you through it.
Our first post of this page contains some data relevant to the importing stage.
There's info and some common questions regarding Wild Area Events here.
To see other Wild Area Events, here.