If you have a Shop-Vac or handheld carpet cleaner, suck up as much urine as possible. If you do not have either of those, use towels to absorb the urine.
Spray with an Enzymatic cleaner such as Biokleen Bac-Out, Kids n’ Pets, or Nature’s Miracle, let it sit, suck up/absorb excess and repeat as necessary.
When dealing with potty training, take couch cushion covers off the sofa, put the cushions themselves in big black trash bags, then put the covers back on.
If there is an accident, you only need to worry about the covers and just changing the trash bags vs. dealing with the cushion as well.
If you don’t have cushions that come off, you can get a cheap plastic shower curtain liner (dollar tree has some) then put a fitted sheet over the couch too.
