My baby is 2.5 months. How to train him to roll over? Any game or play?

Instead of training anything specifically, engage the baby with some essential toys. In a month or so start with tummy time. You can buy these must have toys and books for infants: http://www.gomommy.in/five-must-buy-books-infants/ http://www.gomommy.in/five-must-have-toys-for-infants/