Deepak -- It's not proper etiquette to call out people to answer your question. (At least not at the start of the thread.) Lots of people help out in here, and as you can see, the first response to your question wasn't even any of the people you called out.
As for your question, I would need to see what a date value looks like in your data. That's why Nikher tried to open your workbook. Depending on what the actual format looks like, you will likely use a combination of string functions to pick it apart, and the INT() function to convert those pieces to numbers, and the MAKEDATE function to build the parts into a date value.
String functions can be found here: String Functions
MAKEDATE (and all date functions) can be found here: Date Functions