How to control unwanted thought and worry about future which is not in our control ?
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Perhaps you meant - "..... and NOT to worry about future which is not in our control".
There is very little a person can do to fight his own mind. Trying to control one's own thoughts is like trying to stop the flow of a river with you bare hands - hardly practical and much too far away from what's possible. That being said, I would like to clarify that it is entirely possible to train your mind and achieve certain specific results. But there is a difference between training something and controlling something.
Over the years I have found that it is much easier to leave your mind alone to its own devices. The important thing is that as long as you can command it to get your work done, then it is not really necessary to try to control it. Although if it is becoming difficult to deal with it and your work and daily life are getting affected, then professional help should be sought.
As for me, I don't fight my thoughts and let them freely flow in whichever direction they choose to go. I basically don't fight the flow of thoughts but I do make sure that I don't pay attention to them if I don't need to. It may sound weird and unspecific but for me it’s a regular thing to not interfere if I become distracted by my own thoughts. What I really do is to concentrate on the work that I am doing, rather than 'wanderings of my own mind'.
In the same manner, one can also avoid unnecessary worry over things in the future that we can't control. I do this by concentrating over the present and focusing my energies on what I can affect rather than those that I can't affect.
To sum up my answer to the question:
1. The random thoughts can be ignored by trying not to become entangled in them. Maybe even sit back and enjoy the workings of your own mind ;-)
2. The worry for things in future that we can't affect can be reduced by focusing on the present and making sure that your energies are actively being used for things that you can affect.
This all is obviously much easier said than done but perhaps my words might help you reach a solution that works for you :-)