Actually my problem is I am preparing personal statement and a question hit me. I did my pg diploma in labor laws and after that I practiced with some lawyers who focused on IPR law, now the problem is i m interested in IPR llm so how i should write why I chose IPR rather that labor laws. 

Well you have your answer right there. Although you did your diploma in labour law you then practised with lawyers who were focused on IPR law and this experience made you interested in this field as well. Simply explain the type of work you carried out and why exactly did this field caught your attention? was there any special case you felt interested in? any conversation with those lawyers than charge your mind? what exactly influenced you!
In my case i have been working as a maritime lawyer but nor im doing my llm in public international law focusing on human rights and war law and I explained that my volunteering experience made me decide to focus on this field, etc. I think the best thing you can do is to be honest and just explain the real reason why you like IPR now.
Good luck :)