A lot of people on here have suggested hairspray. Hairspray works because it contains alcohol. Just use rubbing alcohol and it will do the same thing. Also, you can purchase some ink lifting products that are for leather, although most of them will just contain alcohol so it would cost you less you just get the alcohol.
Begin by dampening a white cotton cloth or cotton swab with the alcohol. Don’t use a colored cloth because it can transfer dye to light colored leather. Work from the outside of the stain toward the middle by dabbing with the cloth. Keep the work area small – do not spread the ink into a bigger area!
You should be able to see the ink transfer to the cloth. Dampen a clean area of the cloth or get a new swab as you see ink coming off to prevent re-staining the garment. Gently, keep blotting away until the ink is gone. Do not scrub harshly as that can remove color and a layer of the leather.
Allow the garment to air dry after or between treatments. Once the ink is removed, treat garment with leather conditioner to help it remain supple and smooth.