How to simulate a click onto a dropdown textbox?

[pstein]

A web page contains the following code for an (unexpanded) drop down textbox:

<dt class="border-top padding-vertical-s" accordionloaded="true">      <--- this is an Event
   <span class="accordion__indicator"></span>
some text</dt>

When I click on the arrow down the text box opens and reveals some more text.
The code changes to

<dt class="border-top padding-vertical-s open" accordionloaded="true">   
   <span class="accordion__indicator"></span>
some text</dt>

Mind the added "open" class!
Now I want to open this drop down text box AUTOMATICALLY at loading time.

How can I simulate a manual click on it?

[Ingolme]

None of that HTML does anything on its own. We would need to see what the Javascript code looks like.