Ratchet & Clank Rift Apart Cordelion Armour Part is one of the five collectibles you have to find on the seventh planet alongside the following:
How To Get the Cordelion Armour (Captain Starshield Chest)
The Cordelion Armour Part you can get is the Chest for the Captain Starshield Set. It is found inside the Pocket Dimension in the forge area. The said Pocket Dimension is pictured below.
To get this collectible, first, you’ll need to blow up the forge, then use a Blizon Crystal, which also appears on the map above. In the same room with the crystal is the Pocket Dimension you’ll have to complete.
Get inside, then shoot the yellow floating devices to open them. Jump on the platforms and keep following them to get to the armor. There is also a grappling point here, and you may want to shoot the next set of devices before using the said point.