I would deal with this the same as I would “My couch got soaked with water (bottom section for dirty water”. First dry as much as you can with paper towels, rags, etc, and then flush out as much of the urine as possible with clean water.
Repeat this process more than once. Once again soak up as much of the water as possible with rags, paper towels, etc. It is not only the smell you have to worry about. If left the PH in the urine will slowly start to erode the leather causing it to eventually start cracking and ultimately your leather will become extremely brittle and tear.
