JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post" id="buyvipform" name="buyvipform" class="buyvipform" onSubmit="return zomlink();">

<select name="zomlink" id="zomlink" style="margin-top: 290px;">
<option value="1906083">3 days Trial (2€)</option>
<option value="1906104">31 days (19€)</option>
<option value="1906125">90 days (50€)</option>
<option value="1906146">365 days (99€)</option>
</select>


<input type="submit" value="" style="background:url(<?php bloginfo('template_directory'); ?>/images/vbestall.png) no-repeat; width: 106px; height: 40px; border: 0px;">

</form>

JavaScript

function zomlink() {
  if(document.zomlink.value == '1906104') {
    document.buyvipform.action = 'http://google.com';
  }
     if(document.zomlink.value == '1906125') {
    document.buyvipform.action = 'http://facebook.com';
  }

  return true;
}