I'm not closed minded, and nothing you can say can change my mind.
On a serious note, closed mindedness can harm your mental health - it can prevent you from experiencing things that are necessary to function in society, and basically be a happy person. I think only you can find out how to open your own mind, but you could force yourself (of have someone you know force you) to do something completely different to see if you like any aspects of it. I would have suggested slowly stepping outside your sphere of activities, but sometimes you need a shock. If it is nothing like what you have done before, then it isn't change, is it? It's new. Change is the transition from one state to another, so skip change and just say "that was how I was before, this is how I am now".
Of course, it's not possible to change yourself overnight, but if you think of it like that, it may help. It might not. As I said, only you know yourself. However, by seeing yourself as closed minded, you may now have the motivation to open yourself up.