I am doing a similar position within the First operated Great Western Railway and have just today received my formal offer of employment so whatever I can advise does work! (Just remembered that Scotrail is Abellio now not First haha but still).
Be confident, and make sure you show yourself as a willing and committed person with an in depth knowledge about the key aspects of customer service, why it is important in the rail industry and also have some good wealth of knowledge about the rail industry itself - always handy. Be smart with the interview, come across as intelligent and always able to offer help and advice through that very same intelligence. And one last thing, always ask questions. It's true that rail operators do love people who show themselves as extremely keen and want to know as much as possible.
Like I said, through those key points I am now due to become an Operations Apprentice at Oxford with GWR in September, so lets hope it does wonders for you!
Very best of luck!
Leo Martin