You could try using the magical deodorant stone; or the spray version, if you have it.

Or, as recommended by cat piss experts worldwide: ” … mix in a spray bottle a solution of white vinegar and water about half and half and it will take away the cat urine smell. It works the best and the vinegar odour dissipates in a little while …”

Failing that, how about Hydrogen Peroxide: it cures all known ills.