<!DOCTYPE html>
<html>
<body>
Checkbox: <input type="checkbox" id="myCheck">
<button onclick="check()">Check Checkbox</button>
<button onclick="uncheck()">Uncheck Checkbox</button>
<script>
function check() {
document.getElementById("myCheck").checked = true;
}
function uncheck() {
document.getElementById("myCheck").checked = false;
}
</script>
</body>
</html>