From Bulbapedia, the community-driven Pokémon encyclopedia.
Mr. Garrison (Japanese: タトル Tuttle) is the character of the day for Gotta Catch A Roggenrola!.
He was hired to fix the water pipes in a Pokémon Center. After finding nothing wrong with the plumbing, he suspected that the cause of the water shortage was due the spring that provides water for the Pokémon Center. When Garrison explained that the spring is in a cave that is home to many Roggenrola, Ash, Iris, and Cilan volunteered to investigate with him, having seen a Roggenrola earlier. When they arrived at the cave, they found the stream that runs from the spring to be completely dried up because of a rock-slide that occurred, later to be revealed to be Team Rocket's doing.
After escaping from the cave, Mr. Garrison stated that Roggenrola can find the others through sound waves. Once all the Roggenrola had been rescued from Team Rocket, Garrison returned to the Pokémon Center and contacted the water company about the event. He explained that they would take care of the cave-ins and restore the Roggenrola's home, as well as the spring.