After receiving the mission, head through the now-repaired bridge and proceed to Lyra Forest. As you enter, you'll notice some suspicious activity. Follow the path, and you'll soon encounter members of the Go-Rock Squad attempting to capture Pokémon using their own devices. This is your first direct confrontation with the antagonists of the game.
You'll need to capture the Pokémon they are trying to steal. These captures might be slightly more challenging than previous ones, as the Go-Rock Squad members will try to interfere. Focus on drawing clean circles and using your partner's Field Move if needed to stun the Pokémon. You might encounter Pokémon like Stantler or Aipom here. Continue deeper into the forest, confronting more Go-Rock Squad members as you go.