The personal hotspot has been disappeared in my iphone 4s when i turned on it. how to retrieve it again....

What phone company do you use. There needs to be more information about what is exactly going wrong. Becasue if you are in the USA then the hotspot feature can be turned off and on by the carrier, Such as what Verizon does, if you do not pay for the feature. If that is not the issue then there would have to be a software problem, which there are a few solutions to. One being take it to the apple store and letting them fix it, if it is not an issue with your phone company

Do you have a tethering plan with your carrier? If not, the option will not be available.

How to switch what off. If you dont have the plan then AT&T most likely took the option off your phone. If you dont have it then, call AT&T and add it to your plan and then they will turn it back on, that is what Verizon did when i switched plans. Hope that Helps

If the personal hotspot is turned on and you have the blue bar across the top of your screen, force resetting, holding down the lock and home buttons, will mostlikely cut it off.