2. Talk to the man inside. He will tell you that he needs a Key Card to open the door to the power generator.
3. Go to the Rocket Game Corner. The Rocket Game Corner is located in Celadon City.
4. Go to the far right side of the building and talk to the attendant. She will give you the Key Card if you talk to her and beat the game multiple times.
5. Go back to the Power Plant and use the Key Card to open the door.
6. Go inside and talk to the man. He will give you the TM for Thunderbolt.