Buy a liquid leather repair kit, which can be found at most home improvement and retail stores. Patches are also available, but the liquid gives the best appearance and is easier to use.
Determine which shade of adhesive matches your leather sofa. Most liquid leather repair kits come with a wide variety of colored adhesives, so you should be able to find a match. However, some mixing may be needed to get the perfect shade, as it's important for the colors to match exactly. Mismatched colors will call more attention to the tear, thus wasting your efforts to repair your sofa.
Apply a thin layer of adhesive evenly with a toothpick. Spread out any clumps of adhesive, as the mixture needs to be uniform and cover the entire length of the tear.
Match the grain paper included with the repair kit to the texture and look of your sofa. Apply light pressure to the grain paper, pressing it gently into the adhesive.
Bond the grain paper to the adhesive, using the heat applicator that's included in the repair kit. Press the heat applicator against the grain paper and rub lightly for approximately four minutes, then gently pull back on the paper. Some kits don't require heat, but the bond isn't as strong.