How is humanism important in reformation?

Not very, if you are talking about reformation of religion. It would be like asking how boy scouts are relevant to reformed serial killers.

Humanism concerns itself with how to treat other people with respect, dignity, fairness, and honour.

Reformation of religion is about how to stop treating other people appallingly, and yet still keep the rulebook which says that this is what you have to do.

If you want to treat other people well, and that's your only aim, then learn about Humanism. If your religion tells you to murder/torture/abuse other people, and you're not comfortable with that but don't want to give up the religion, then get yourself a reformation.