Not sure if this will help you or not, but what you need to find is how to change the selected value in a select2 field and then work out how to alter it to make it work in ACF. This looks promising. http://stackoverflow.com/questions/19639951/how-do-i-change-selected-value-of-select2-dropdown-with-jqgrid. I do know that you might need to target the hidden field, but that’s just a guess.
There isn’t any list that I know of that explains how to get or set values in all of the different ACF field types.
