If Rotom only knows its signature move upon reverting to its default form, it learns Thunder Shock to avoid having no moves. Appliances for switching Rotom's form can be found in the following locations, depending on the game: Platinum: In the Team Galactic Eterna Building. Requires a Secret...
After catching Rotom, players will get the Secret Key, which is needed to open the secret Rotom Room inside Eterna City's Galactic Building. Here, players can change Rotom's form by accessing the myriad of appliances available there. More: Pokémon: How To Receive Mystery Gifts In Brilliant ...