Remove the selected options :
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$('#mySelect2').val(null).trigger('change');
============================================
Completly remove the select2 initialization :
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$('#payment_method').html('').select2({data: [{id: '', text: ''}]});
Example 2: select 2 select a value
SELECT2 V4 :
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For select2 v4 you can append directly an option/s as follow:
Or with JQuery:
---------------
var $newOption = $("").val("TheID")
.text("The text")
$("#myMultipleSelect2").append($newOption).trigger('change');
other example :
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$("#myMultipleSelect2").val(5).trigger('change');