HTML Multi Select Options

Question

I have this multiselect dropdown 

 

<select id="ddlCustomers" class=" form-control input-sm selectType country" name="ddlDtype" multiple="multiple" size="7" > 

when user selects  multiple options Example 2,3,4 

Then I am saving like this  

var countries = [];

$.each($(".country option:selected"), function(){

countries.push($(this).val());

});

 and  save to DB 

with var country= countries.join(", ");

 

Now when a user comes & edits these multi-select saved values  I want these pre-saved options 2,3,4 should be selected & rest in the list to be unselected so that the user can modify its choice & can select any other items from the option 

 For saving, I have bootstrap modal pop with this HTMLselect option & other controls. after save they appear in a grid view, in grid view on each row id user can edit the select options in another modal pop and saves edited values in DB. 

Please help