<!DOCTYPE html>
<html>
<body>
<form>
What color do you prefer?<br>
<input type="radio" name="colors" id="red">Red<br>
<input type="radio" name="colors" id="blue">Blue
</form>
<button onclick="check()">Check "Red"</button>
<button onclick="uncheck()">Uncheck "Red"</button>
<script>
function check() {
document.getElementById("red").checked = true;
}
function uncheck() {
document.getElementById("red").checked = false;
}
</script>
</body>
</html>