To restart the console, press the Power Button for three seconds and then select to Restart. Make sure that Pokémon: Let’s Go, Pikachu!/Pokémon: Let’s Go, Eevee! has the latest software update.
From your Switch’s home screen, select System Settings. Find Data Management and Delete Save Data in the sub-menu that appears on the right side of the screen.
To delete the game, go to the main screen and press Up, Select, and B at the same time.