Whether the tear is on the inside or outside, you can fix it with glue. It’s important to use a glue that is made for leather. If the tear is on the inside of the jacket, use a leather glue. If the tear is on the outside, use a fabric glue.
You can fix leather jackets and boots by using a simple patching kit. The kits are available at most leather stores and all you have to do is apply the glue to the tear and then press the patch over the tear. The kit comes with a few different sizes for different sized tears and you should choose the one that best fits the tear.