Try opening the RoboHelp HTML application (not the RoboHelp for Word application used to create the .HLP file). There create a new project specifying to import the HLP file. From memory that does a pretty good job of bringing across the content. Once there it is easy to create a CHM file. If you need to know more specifics, you'll need to tell us which version of RoboHelp you have.
we are trying to generate .chm because we are migrating the application to 64 bit from 32 bit and those help files must also be changed from .hlp files.we want to know how to link the generated .chm files with that application?..
OK. Now the scope of your original question has expanded to making sure your applications calls it correctly! There are so many questions that I or someone else would need to ask and get answers to that it makes little sense to continue this thread. As I have said before, what you want is a lot of training and hand holding. This takes time. If you are not able to spend the time to learn how to do what you want, please don't expect someone else to do it for you free of charge. All of us who offer advice here are paid employees or freelancers. Whilst we do not mind offering free advice where we can, sometimes we simply can't. This is one of those situations.
If you want me to help you further you can contact me via my website. However I will not be in a position to do anything straight away.