it already has one equipped.

Learn how to equip items to your Pokémon in Diamond and Pearl. This guide explains how to manage your Pokémon's held items, even if they already have one equipped.

So, you've got a Pokémon holding an item, but you want to give them a different one. Maybe you found a Rare Candy and want to give it to your starter, or perhaps you just want to swap out a Sitrus Berry for a Lum Berry. No problem!

When you try to give a Pokémon an item that it already has equipped, the game will tell you, "It already has one equipped." This just means you can't give it a second item. You'll need to remove the current item first before you can give it a new one.

Here's how to do it:

1. Access your Bag.
2. Select the Key Items or Held Items pocket (depending on where the item is stored).
3. Choose the item you want to remove from your Pokémon.
4. Select the option to Take the item.

Once the item is back in your Bag, you can then give your Pokémon the new item you wanted to equip. Easy peasy!