How to get cat pee smell out

I was in the hospital for about two months. One of my cats started peeing in the cashiers “for no reason” while I was gone. I left my 18 yr old to care for my two cats. When I got home, I found out that the litter boxes had been completely neglected, so it’s obvious why she was peeing elsewhere. The problem now is that the carpet in the basement absolutely stinks. Does anybody have any tips for how I can get the smell out?

And yes, we have talked to the vet. She is OK and the problem is solved. It’s just the smell.