What to do with lift key in celadon city tower?

In Celadon City Tower, the lift key is used to access the elevator that leads to the upper floors of the tower. You need to locate the lift key, which is typically found by defeating Team Rocket members inside the building. Once you have the key, head to the elevator, use it to reach the floors where you'll encounter more Team Rocket activities, ultimately leading you to confront their leader and progress in the game.