Use propyl alcohol, like you do for removing permanent marker pen stains.

Bleaching agent would likely render everything white, including the colour(dye) of the leather.
Eraser removes ink marks by abrasive action which would affect your leather.
You need a solvent which can dissolve the ink but does not affect the colour of the leather.
You can try out using alcohol on an area of leather which is hidden to see if it affects the leather.