The neatest repair work will require you removing the seat covering so you can work from the underside.
You need to pull the torn edges together. This is best done typically with thread. In the fur business, dental floss is the thread of choice because it doesn't rot and is quite strong. Chose a color that is least visible. Neat individual suitures, not a running chain stitch! Knot it on the underside for less visibility if you chose to let this be your sole repair.
You can go further with a patch and adhesive, again attached to the underside. Sew it up to pull the edges together, and they apply a large patch with an adhesive. I find liquid thread to be quite good. Once the adhesive has dried, you can cut and remove the suitures. In this case, it's advisable to have the knots on the top in order to facilitate removal. You can also fill the gap between the edges of the leather with the adhesive in order to hold them together, but this usually isn't a satisfactory approach.
