How can I remove old cat urine smell
You have to replace the carpet. Cat urine smell won't go away no matter what you use.
I had success with Breathe Green charcoal packs and leaving the windows open
It was not in carpet.
Resolve pet urine carpet spray.
White vinager let it soak
Everything you need to know here: https://www.craftylittlegnome.com/whole-house-smells-like-dog-urine/
These might help: https://amzn.to/2SkswNH