<input type="radio" name="model" value="item1" id="item1">
<label for="item1">item1</label>
<input type="radio" name="model" value="item2" id="item2">
<label for="item2">item2</label>
<input type="radio" name="model" value="item3" id="item3">
<label for="item3">item3</label>
<select name="select_model" id="">
<option value="item1">item1</option>
<option value="item2">item2</option>
<option value="item3">item3</option>
</select>
const select = document.querySelector('[name="select_model"]');
const radios = document.querySelectorAll('[name="model"]');
select.addEventListener('change', ({ target: { value } }) => {
Array.prototype.find.call(radios, n => n.value === value).checked = true;
});
radios.forEach(function(n) {
n.addEventListener('change', this);
}, e => select.value = e.target.value);