JSFiddle - React, Tailwind, and code Playground

HTML

<a class="btn" id="reg1" rel="btn_region" href="#">Выбрать №3</a>
    <a class="btn" id="reg2" rel="btn_back" href="#">Выбрать №1</a>
	<br><br>			
	<input type="radio" name="radio-set" id="st1"/> №1    
	<input type="radio" name="radio-set" id="st2"/> №2

JavaScript

$(document).ready(function() { 

		$("#reg1").click(function() {	
			$("#st2").attr("checked", "checked");
		});
		
		
		$("#reg2").click(function() {	
			$("#st1").attr("checked", "checked");
		});			
});