Loss of engine power on Forester

A friend sent me this link on cleaning them out, but I am doubtful on that:  https://cr4.globalspec.com/thread/126214/Cleaning-a-Catalytic-Converter

I ordered the Walker 54573 on Amazon.  I'll notify david who I bought the Forester from who said it was the biggest expense he had two years ago that it clogged.  He may be able to get something back.