How to Evolve Pikachu
You cannot evolve the Pikachu from the Pokemon: Let’s Go, Pikachu! data. Thus, you need to catch a Pikachu in the wild to evolve it. Once you catch a wild Pikachu, get it to at least Level 15. Then, use a Thunderstone to evolve it into a Raichu. The Thunderstone is rare, but the duo digger brothers can sometimes dig them up in the Wild Zone, near the Nursery.