Add Menu Class to First Child (Page Menu)

Hi, I am hoping someone can help me out. I am trying to add a unique id and class to the first drop down of my menu on https://www.designremedyinc.com/indyme to expand the width and make it into 2 columns. My thought is to add a class just to that first ul class=”children”. I was able to find some code online to add add_menuclass function however this adds the class to the first

I tried to change the code below to

function add_menuclass($ulclass) {
return preg_replace(‘/

/’, ‘<ul id=”solutions” class=”dropdown”>’, $ulclass, 2);
}
add_filter(‘wp_page_menu’,’add_menuclass’);

Thinking that $ulclass, 2 would address the second

this works for the first

but not the second. Any help would be greatly appreciated.

Thanks