Is it true humans can be turned into jinns?

I believe what you mean is 'Can Jinn take on human form?' the answer to this restructured is yes along with possession. However if you mean can a human person become a shaiytaan this is possible because a shaiytaan (devil) is more a title as one who commits murder is a murderer, one who tells lies is a liar, and one who does numerous evil things becomes a shaiytaan(devil). this applies to both man and jinn.