p0420 catalyst efficiency below threhold bank 14

I was wondering what I can do about this code so I can pass emissions. What part(s) do I need to replace and is it easy enough to do it myself?(Code P0420)

That is a cat efficiency code, so I would assume something would need to be done with the cat.

Well, could be that the cat is worn out. Replace it with an universal unit(They are not that expensive)