This is a Wild Area event held by Sword and Shield. This event hosts Gigantamax Grimmsnarl and Gigantamax Gengar.
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 would contain 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.