Prepare the couch to be restored. If you chose to do anything more comprehensive than simply purchasing a leather recoloring balm, the couch will need to be prepared for restoration. If leather is dirty, clean it with warm, soapy water or with a leather-cleaning solution.
Wipe down the back and the sides of the couch with diluted rubbing alcohol on a clean white cloth.
Wipe the rest of the couch with leather prep. Pour some leather prep on an abrasive pad if the sofa isn’t badly cracked. If there is substantial cracking, use a clean cloth instead, since an abrasive pad would only worsen the cracks on the couch. Rub until the color from the couch begins to show on the cloth or the abrasive pad. This indicates that the finish has been removed.
Wipe or spray the couch with diluted rubbing alcohol or another alcohol cleaning solution. This will remove any silicones that the leather prep could not dissolve.
Wait half an hour for the leather prep to dry and evaporate.
Apply a light filler, which will hold the leather together in order to prevent future cracking, with a sponge to repair thin cracks. Apply only a thin coat, and allow it to dry.
Sand the leather with fine sandpaper to remove any excess filler.
Repair bigger or deeper cracks with a leather repair compound. Smooth the compound over the seating cushions of the couch using a palette knife, and allow it to dry for at least half an hour.
Sand the areas where repair compound has been used with fine sandpaper.
Use another coat of light filler if necessary.
Shake a bottle of leather colorant for several minutes to ensure that is mixed well.
Rub a thin coat of colorant into the sofa, using a sponge. This will provide a base for the brown color that will sprayed in the next step. Press gently. Do not apply too much pressure.
Wait for the colorant to dry, then use a spray gun or an airbrush to apply the restorative color to the couch. Practice on paper if you have never used a spray gun or an airbrush before. Allow the color to dry between coats.
Use a sponge to gently apply thin layers of finish to the couch. It is recommended by some leather restoration companies, like the United Kingdom-based Furniture Clinic, that two layers of glossy sealant and two layers of finish be added to leather furniture.