Fill a small bowl with one part white vinegar and two parts food-grade linseed oil.
Dip a white, lint-free cloth into the solution and wipe the couch with the cloth in soft, swirling motions that overlap. Re-dip the cloth whenever it begins to feel dry.
Leave the solution on the leather for 24 hours. The leather will absorb the linseed oil, which acts as a natural moisturizer.
Buff the leather dry with a second white, lint-free cloth. Wipe the surface of the couch firmly in a circular motion to remove any remaining solution.