Please help me to prepare a letter
I am a warehouse superviser at one of the leading spareparts company
I can't handle that job. Too much head ache,difficult .before 1 month I am an assistant superviser I like that job. I like to returnback my old position.

Often it is never really possible, they will have already hired a replacement for your old position.

But instead of letter, my advice is just go talk to your boss about it.

I agree with Chuck. Talk to your supervisor rather than writing a letter which will be on file maybe as long as you ever work there.
Depending on how understanding or not understanding your employer is, this may not be looked upon favorably. And if they have found or have someone in mind to fill your old position, your current job could be put in jeopardy. If you are saying that you have tried that new job for only one month, it is not long enough to really assess the position. If the headaches you are encountering are the behavior of the people you supervise (usually a big part of it), maybe more leadership on your part is needed and/or maybe you need to discipline or get rid of some of them and maybe that is why your company put you in your position. Don't take this step (asking to be relieved) until you have given it a lot of thought.