How do you evolve DUNSPARCE on Pokemon diamond ds?

You can't evolve Dunsparce in Pokémon Diamond. It's one of the few Pokémon that doesn't evolve in the game.

However, in later games, Dunsparce gets a new evolution! In Pokémon Legends: Arceus, you can evolve Dunsparce into Dudunsparce by leveling it up while it's holding a "Shedinja" item.