You would do it with Javascript
Place an onclick event on the button, which calls a Javascript function which reads the value configured in the select, and based on that select value it opens the desired URL.
// event.preventDefault() kills the submit form event triggered by pressing the only button in the form (default in some if not all browsers)
// jump is the function
I guess you could use onchange to auto jump without having to press button.
<!DOCTYPE html>
<html>
<body>
<h1>Select</h1>
<br>
<form>
<select name="choose">
<option value="1" selected>One</option>
<option value="2" >Two</option>
</select>
<button name="openlink" onclick="event.preventDefault(); jump();" >Go</button>
</form>
<script type="text/javascript">
function jump() {
// arrays start from 0, and used values 1 and 2 in the select
var urls = [ '','[url]https://www.google.com[/url]' , '[url]https://www.linustechtips.com[/url]']
var element = document.querySelector('select[name="choose"]')
var id = parseInt(element.value) // get the value of the select element
console.log(urls[id]) // press F12 to open developer tools and you see it logged there
window.open(urls[id],'_self') // use _blank to open in new tab
}
</script>
</body>
</html>