Install Pokémon GO and Pokémon HOME on your device
Sign in to both apps with the same Nintendo Account
Open Pokémon GO
Tap the Poké Ball
Tap Settings
Scroll to Pokémon HOME
Sign in to your Nintendo Account if prompted
Select the Pokémon you want to send
Confirm the transfer
Open Pokémon HOME
Receive the transferred Pokémon in the GO Transporter section
Note that transferred Pokémon cannot be sent back to Pokémon GO