Thank you for tips! I don’t know where to find a patch that matches the jacket’s leather. What if Put something like an embroidered patch over it? Or better just try and find a similar material to glue it together instead?
Hm… if you can’t find an almost identical piece, whatever you do, you better do it on both sleeves, so it looks like it’s part of the design, not a patch.
If you can’t find something that even closely resembles the leather on your jacket, take any piece of leather that’s light colored, but darker than the color of the jacket, make some zig-zag stiches on the edges of the piece (kind of like a decoration, use a thead that is almost the same color as the piece or the jacket, not something in between) and just glue that over the torn part from the front side. Use rubber based adhesives, they work best with leather. Then, do the other sleeve as well (for symetry). Stitch over the patch in any way you like, to add a bit of robustness to the patch.
And that should be about it.
