Just go to the party and engage with people. Actually be interested in who that person is, what they think, and how they spend their time. People are fascinating, even the grouchy boring ones.

Advice like this article, and the thousands of books before it, are usually totally garbage. I'm very introverted. I've spent weeks by myself in nature, completely alone. I find parties too stimulating. But just do it. It's not like you're getting your arm cut off. You're just talking to people. Don't be mad at yourself for saying some out of pocket stuff. Don't dwell on what you could have done. Just see what's going on in the lives of other people and stop overthinking it.