~たいことがある ('there's something I want to') is a polite preface for raising a request. The second sentence stacks several politeness markers: ちょっと (softener 'a bit'), お願いする (humble 'to ask'), ~てもよろしいでしょうか (the most polite form of 'is it OK if I'). よろしい is a respectful version of いい. A textbook polite request.