Buff small scratches with a soft cloth. If this doesn't erase the marks, add some leather conditioner to the cloth and rub it over your couch.
Apply a bit of leather prep to a scrubber, and rub it over the couch's surface. This will remove the leather finish, including surface cracks, leaving a dull, smooth layer.
Use a palette knife, and apply heavy filler to badly cracked spots not removed with the leather prep. Wipe excess filler away with a soft cloth so it only stays in the cracks. Let the filler dry for at least five minutes, then smooth the target area with fine-grit sandpaper.
Shake your leather dye for three minutes. Dab a little bit of the dye onto a sponge, and work it into the grain of your leather couch. Wipe away excess dye with the sponge, and allow the dye to dry completely. If cracks still show after the couch dries, add more filler and apply more dye over the filler.