How can I socialize?

I spend my whole day in a cycle of university, home, work and sports, I can't socialize, I want new people to enter my life but I don't know where to go, in my free time I can only sit in parks and relax, how and where do you socialize? Even if I attend events, I can't be very assertive about socializing because everyone hangs out with their friends, "they already have friends, why would they want to get to know me?" I think.
How can I socialize?
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