When someone is turning the bike,what will be a natural way to say that ( not left or right but around).
Do you know how to turn a bike?
Do you know how to turn a bike around?
What sounds natural ?
To me turn a bike suggests picking up a stationary bike, and putting it down facing the other way.
The word I would use for causing a moving bike to change direction is steer, not turn.
If the bike is going west, and you want it to go east instead, you could ask:
Do you know how to make a U-turn on a bike?
A U-turn is a 180 degree change in the direction of a vehicle's motion. Unless the vehicle can "turn on a dime", the path of the vehicle's motion is shaped like a capital letter "U".
If it is clear from the context that you are talking about riding bikes, you can omit "on a bike":
Do you know how to make a U-turn?