$(function(){
alert('Hi');
$('iframe[title=TestPageResult]').css("height", 200);
});

<style>
.frameHeight {
height: 100px !important;
}
</style>
<script>
 $(function(){
  alert('Hi');
  $('iframe[title=TestPageResult]').addClass('frameHeight');
 });

console.log($('iframe[title=TestPageResult]'));

<iframe frameborder="no" height="300px" id="0660Y000004tr0j" marginheight="0" marginwidth="0" name="0660Y000004tr0j" scrolling="no" title="TestPageResult" width="100%"></iframe>