Get a rotom
Use the Rotom you caught in diamond, pearl and platinum.
bring rotom and make sure he is first and go in the elevator and you will see rotom forms
Get a Rotom and go in the elevator and Boom B1
In HeartGold and SoulSilver, you can access the 1st floor of Silph Co. as soon as you enter Saffron City however you can't go into the elevator in order to get to the 2nd floor unless you have a Rotom as your lead Pokemon.
Get a rotom
Use the Rotom you caught in diamond, pearl and platinum.
bring rotom and make sure he is first and go in the elevator and you will see rotom forms
Get a Rotom and go in the elevator and Boom B1
In the Silph Co. building in HeartGold and SoulSilver, in order to gain access to the second floor, Steven Stone cannot be in the lobby and you also must have a Rotom be the lead Pokémon in your party.
In HeartGold and SoulSilver, you can access the 1st floor of Silph Co. as soon as you enter Saffron City however you can't go into the elevator in order to get to the 2nd floor unless you have a Rotom as your lead Pokemon.
go on an elevator
Use the portals or the elevator.
You need a rotom as the first Pokemon in your party and he will open the elevator 4 u. (Untested but have seen it irl (in real life)
Go up the elevator.
you must have rotom first in your party then talk to the elevator
(Well if you REALLY want to know.....)The game acts like its impossible to get into the elevator. BUT hidden if you bring a Rotom at the front of your party and enter Silph Co. no one is there. (Mysterious) If you click the elevator you will go in and you go through some dialogue and you will see a room with 5 devices. You can choose which machine rotom will go into. You can also learn that specific machines move. You can change or revert to any form just by going there.