Test the leather in an inconspicuous area, give it a good wipe with a wet cloth, see it the leather absorbs the moisture, if it impervious to wetness then more than likely it ok to continue.
Then try wiping it off with a damp cloth ( it might be that simple)
Dip a cotton bud into a solvent then roll the head of the bud over the ink, then check for transfer.
You are trying to dissolve the ink without touching the leather, I use a very fine paint brush to apply the solvent.