This is a Wild Area event held by Sword and Shield. This event hosts Gigantamax Hatterene and Gigantamax Corviknight.
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.
Index 059 has Hattrem encounters with the Gigantamax factor. It appears that it may be unattended, as Corvisquire does not get the same treatment.