Being gay/lesbian/bi/trans (etc) is not a choice. It isn't something which will be 'overcome' through religion, fasting or therapy. A heterosexual person would argue that nothing would 'turn' them gay; it is the same for gay people who try and 'turn' straight. You can't switch or change who you are. Also, i don't see why you would want to change someones identity.
Being homosexual or transgender is not an illness or a disorder. It is something deep down in a person's DNA, something that simply cannot be changed. This is something a person is born with, even if they haven't always recognized their feelings. We need to spend less time trying to figure out how to change homosexuality and spend more time learning to embrace all people for who they are.
Since the beginning of time, people have been born homosexual. It is not any different than a person being born with brown hair. It is not something that can be cured. There are historical records of people being homosexual in very old societies. It is nothing new to the modern era.
There are ways to train and adjust people's behaviors and choice making skills. However, when it comes to someone's sexuality, the basic drive which decided if they are hetro- or homosexual is inherent in them and can not in and of itself be changed. You can associate these thoughts and behaviors with rewards or punishments but the source can not be changed.
No, homosexuality cannot be treated or changed. Conversion therapy that aims to convert homosexuals into heterosexuals has been proven harmful many times. It is a barbaric practice that has been rightfully outlawed in many places. Regardless of whether one believes homosexuality is congenital or learned, it is not a condition that can be changed.