I changed the field type to post_object with multiple values enabled for aesthetic reasons. A lot of trial and error and digging found that this works to dynamically change the selected values…
var selector = '#acf-field_5f1f49df49567-field_5f33ff4c31a81';
$(selector)
.empty() //empty select
.append($("<option/>") //add option tag in select
.val("2514335") //set value for option to post it
.text("Red")) //set a text for show in select
.append($("<option/>") //add option tag in select
.val("2514356") //set value for option to post it
.text("Blue")) //set a text for show in select
.val(["2514335","2514356"]) //select option of select2
.trigger("change"); //apply to select2
