According to the official Pokemon website, “You will be able to receive this special Meowth by selecting the Get via Internet option in Mystery Gift.”
This special Gigantamax Meowth is available to all players as an early-purchase bonus.
This Gift will be available from Friday, November 15, 2019, to Wednesday, January 15, 2020.
Those without a Nintendo Switch Online membership can still receive the gift as long as their Switch is connected to the internet during that period of time.