If you know the Index, Value or Text. also if you don\'t have an ID for a direct reference.
This, this and this are all helpful answers.
Example markup
Using jquery-2.1.4, I found the following answer to work for me:
$('#MySelectionBox').val(123).change();
If you have a string value try the following:
$('#MySelectionBox').val("extra thing").change();
Other examples did not work for me so that's why I'm adding this answer.
I found the original answer at: https://forum.jquery.com/topic/how-to-dynamically-select-option-in-dropdown-menu