How do you remove pen from a leather car seat?

If you mean ball point pen, take a bottle of cheap hair spray, and give the ink mark a spritz. Let it sit a moment , and wipe with a soft cloth. This also works with machine washable clothing - spritz the ink stain and launder it.

I have just removed 100% of the black pen marks from our cream leather couches by spraying my french parfum and rubbing it in. You must not let it dry and rub fast, otherwise you'll strip the leather tan and there will be light spots left on the furniture.