Instructions
Go to Route 10 outside the Rock Tunnel and enter the Power Plant. After speaking to everyone inside, a guard informs you that a part was stolen from the Power Plant, which you must return.
Return to Route 10 and continue along the path to Cerulean City. As you enter the city, a Team Rocket member runs past you.
Continue through the city until you reach Route 24. Talk to the Team Rocket member standing by the bridge. When he challenges you to a battle, defeat him with your Pokemon team. You are told that the Power Plant part is hidden in Cerulean City.
Return to Cerulean City, and enter the Gym. Go to the top left corner of the gym. Press "A" while standing in front of the buoy to receive the part.
Go back to the Power Plant and speak to the man inside to return the part. Exit the building, and head to Lavender Town.
Enter the Lavender Town radio tower. Talk to the man standing by the stairs. He will give you the expansion card as a reward for restoring the power. This card gives your radio the ability to tune in to the Poke Flute channel.
Go to Route 11 and walk up to the Snorlax blocking the path. Open the game's menu and select "Radio" from your Poke Gear bag. Change the channel to Poke Flute by moving the dial to the upper-middle area of the radio. The music awakens Snorlax. Talk to him to fight.