My Citizenship has been changed after H1B approval.. pls help???

My citizenship has been changed from Indian to British after H1B approval. When I was applying initially H1 I have submitted my Indian passport to the employer now I need to attend my H1 visa but my Indian passport is not valid anymore as I have taken up British citizenship. Do you need to fill any different form to let visa officer know about this change?? is there any process before I attend for the visa. Let me have your thoughts please…