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

don't train. he will do so on his own. he still needs support to hold his head. so don't push him to turn over. vital organs are still being formed or getting strengthend. so don't go against nature and make a mess of things. generally a baby starts to turn over by mid 3rd or 4th month. so wait and have fun....