The Name Rater can be found on the ground floor of the Eterna City Condominiums. You’ll have access to him and his services soon after winning the Coal Badge from Roark in the Oreburgh City Gym.
This NPC allows you to change any Pokémon’s nickname, provided you are the Pokémon’s original trainer. This is the only way Pokémon nicknames can be changed in Platinum.
Where To Find the Name Rater
The Name Rater is on the first floor of Eterna City’s Condominium building.
You’ll be able to find him very early in the game, just a short time after defeating Leader Roark at the Gym in Oreburgh City.
To locate the Name Rater, start at the Eterna City Pokémon Center and head south.
Turn eastward when you reach the Poké Mart.
Then at the end of the lane here just enter the Condominium building to your north.
The Name Rater will be at the table to your left as soon as you enter the building.
Changing a Pokémon’s Nickname
Changing a Pokémon’s nickname is a simple process.
First, speak to the Name Rater with a Pokémon in your party whose name you would like to change.
Note: The Name Rater will only change a Pokémon’s name if you are its original trainer—the nicknames of Pokémon that are traded to you are permanent, whether the Pokémon comes from an NPC or another human player.
Select “Yes” when he asks if you want him to rate one of your Pokémon’s names.
The Name Rater doesn’t actually give any constructive ratings—to him, all of your Pokémon’s nicknames will be “decent.”
But then he’ll ask if you want him to change the selected Pokémon’s nickname to a better one.
Pick “Yes” again and the naming screen will pop up. Just enter the new nickname and hit OK.
The Name Rater will inform you that the change is complete.
Thanks to the Name Rater, you won’t need to worry about picking perfect nicknames—as long as you’re the original trainer, you’ll have unlimited do-overs.