I just went to Milan for traveling and bought some items there, the shop assistant said I can get a tax refund by asking the train manager for a customer stamp. For the train manager, they said that it’s the person who asks me to show the passport. But the condition is, when I went back from Milan to Lausanne, nobody ever asked me for my passport, and I have no idea where I can get the customer stamp so that I can get the refund.