How Do I clear Google Custom Search Index data (Urls & sitemaps)?

I had setup a Google custom search for my website but after a few months I started using that domain for something else and the data that was there exists no more, the worst that is happening right now is that the Google search engine is still having the data that was present there before(the sitemaps and the urls) and I dont know how to completely remove/delete them? Help me out please