They sell stain removers for leather: https://www.furnitureclinic.com/Leather_Ink_Stain_Removers
This is Linda. Leather stains are notoriously difficult to remove, however you can try lemon juice and Cream of Tartar. Here's an article that can guide you. Wishing you success.
Depends what it is...
Martha,. Use Saddle Soap, you can find it at an automotive store, follow directions on the can. Aloha!