Try a Mr. Clean Magic Eraser. Wet the white part of the sponge, and squeeze till it is just damp. Rub the sponge gently (no scrubbing ) on the stain's surface until it is clean. Pat it dry with a clean white cloth.
Use Isopropyl alcohol if the Magic Eraser doesn't work. Dampen a cotton cosmetic pad or white cotton cloth with Isopropyl alcohol. Dab the leather in a small inconspicuous area to test. If there is no discoloration, proceed with the next step.
Dab the leather with the cloth in a small area, working from the outside to the inside in a circular pattern.
When you see the ink transfer to the cloth or pad, dampen a new, clean area of the cloth or get a new pad.
Keep blotting until all the ink is gone. Don't scrub hard as leather is sensitive, and you don't want to damage the surface.
Let the leather air dry.