Hey don't do anything...the baby will automatically do it when the body is prepared ....just keep watching the moves .;

When he is on his back he rolls over on his tummy and then tries to push himself forward. Since he is unable to do so, he ends up going round in circles and starts screaming coz he can’t move ahead

He has already rolled

Let him try. He will succeed. Put some moving toy in front of him. But honestly I think at 4 months crawling is a bit too early. He must be trying to roll.