Open the windows and allow fresh air to enter the room, especially if the smoke itself is relatively recent.
Place saucers containing vinegar and charcoal in the room to absorb any smoke within the vicinity of the couch.
Wipe the couch's entire leather surface with a slightly damp cloth, wiping it multiple times to ensure you remove as much of the smoke residue as you can, then let the sofa dry.
Unzip and remove the leather covers from the cushions if possible.
Scrub the leather surface of the cushions and the remainder of the couch using a leather cleaner and soft brush. Spray the foam insides of the cushions with pet cleaner spray and reassemble the cushions.
Pat the leather with a dry cloth to absorb any cleaner residue out of the couch and then buff the couch with one more dry cloth.
Spray the couch's surface with a fabric refresher such as Febreze.