Leather is not very porous and in many cases the contamination will have flowed right off the surface. In this case just spray Anti-Icky-Poo on the leather and you’re done. For leather couches or chairs, most likely the contamination has flowed into the cracks, which makes it slightly more difficult to treat.
Just lightly pour the product following the same path the contamination has taken allowing the Anti-Icky-Poo to roll off into the cracks the same way. If the contamination has soaked into the couch or chair past the leather covering and you need to inject, try to inject into the seams.