The biggest and most important step is realising you have a problem and wanting to change. I was a bit like what you describe during high school and late teens,

The biggest and most important step is realising you have a problem and wanting to change. I was a bit like what you describe during high school and late teens, but I saw it not only affects my personal relationships - it doesn't align with my moral code. It's very hard to recognise narcissism in yourself, but you have done it. I'm pretty sure from here the way to overcome it is straightforward. And don't beat yourself up too much, everyone has a bit of narcissism in them, you just have a bit too much. You will work through this - I'm sure.