Surf is a move that is typically learned by Water-type Pokémon, and Pikachu is an Electric-type Pokémon. While Pikachu can learn other moves like Thunderbolt, Thunder, and Quick Attack, it cannot learn Surf.
It's possible you might be thinking of a different Pokémon game, a spin-off, or a special event where Pikachu might have access to Surf for a limited time.
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