How do I get a biro pen mark out of a leather chair?

Omg I was doing my homework and i don't know how but I accidentally got a big biro mark on the new leather chairs my mum bought and they were quite expensive, she loves them and seriously she would tell me off and get a bit upset, luckily she hasn't seen it yet but PLEASE!!! anyone know how I can get it off? I tried this mr muscle kitchen cleaner thing and it didn't work and I tried nail polish remover too, luckily it didn't damage the leather lol and the leathers light so it looks so bad. Sorry about nagging so much, thank you to everyone who answers!