I don’t think Homecoming King is that notable of an achievement for colleges as it is mostly a popularity contest.
But, I can understand how that it is important for you, so you can write it in an essay, your transition from being unsocial to Homecoming King, if that applies to you.
But, the main way to show that you are social are through teacher recs who say how you are an active participant in class, your EC’s which show your involvement in the school and community (how you’re not a “nerd” who just plays videogames at home), and possibly the interview in which the interviewer can see how outgoing you are and write in in their report.