Great to see Pikachu Surfing again!
Junichi Masuda, game director of Pokémon Let’s Go has appeared in the variety show, Pokenchi (Gathering at the Pokemon House) this morning with some new footage to show.
In battle, Pikachu uses a Water-type move called Splash Surf. Outside of battle, his board doubles as the surf move, Water Walk. It was also confirmed during the segment these special field moves (like HMs) will not take up move slots.
During this same segment, Eevee was shown using a new fire-type move called Flare Burn. More about this in Serebii.