A forked, metal rod worth at least 250 gp, attuned to a particular plane of existence. PhB 245, emphasys mine.

The metal rod must by attuned to a particular plane of existence, does that means that the rod has to be crafted on that plane? Or worked somehow on that plane?

If the answer is no, and the component is not considered a magic item, a PC should be able to build it with the Crafting downtime activity in 50 days.

Can the PC build a metal rod attuned to Carceri and banish creatures to oblivion?

A forked, metal rod worth at least 250 gp, attuned to a particular plane of existence. PhB 245, emphasis mine.

The metal rod must by attuned to a particular plane of existence, does that means that the rod has to be crafted on that plane? Or worked somehow on that plane?

If the answer is no, and the component is not considered a magic item, a PC should be able to build it with the crafting downtime activity in 50 days.

Can the PC build a metal rod attuned to Carceri and banish creatures to oblivion?