A transgender young woman has to dress up as a man to rejoin a boy band she was fired from.

Is there any reason as to why she does this?

Structure: A [what] young woman [must] dress up as a male to join a boy band [because why].

Comedy loglines work best if there is a sense of irony included, so for example, “a transgender woman must dress up as a new man in order to rejoin the boy band she was fired from,” would work a bit better because the irony of one turning transgender – only to subsequently pretend to be the gender they were born as – subtly hints at the stakes of the story.

Find something that suits your character so that it can help juxtapose against the grain of your premise. Just remember that stakes are a must for loglines, whereas irony is a key to comedy.