Instructions
Take the elevator to floor five, then head left and down. You will eventually see a warp square.
Take the warp square to floor nine and head right. Pick up the Card Key so you can open the many locked doors in the Silph headquarters.
Take the elevator to floor three. Use the Card Key to open the door on the left.
Take the warp square to floor seven and fight Gary, who will approach you automatically. Most of Gary's Pokemon have fully evolved and have an average level of 40.
Take the other warp square to floor 11 and fight Giovanni to banish Team Rocket from Saffron City, allowing you to fight Sabrina and earn the Marsh Badge.