Mix one cup of vinegar and two cups of linseed oil in a bowl. If you do not have linseed oil, you can substitute extra virgin olive oil.
Wipe the solution onto the couch, swirling on in a circular motion with a soft cloth. Leave the mixture on the couch overnight.
Dip a soft cloth in warm water and wipe the entire couch. Pat dry with a towel to remove excess moisture.
Apply a leather recoloring balm to the couch with a soft cloth. Recoloring balms come in a wide variety of colors; you may need to mix several colors to match the shade of the couch.
Remove excess balm with a soft cloth and buff the entire couch. Buffing will set the pigments in the recoloring balm and give the leather an attractive sheen.