Update selectbox entry programmatically

I’ve implemented a dropdown that is selectBox in my node js workflow. I have selected one value from that dropdown and then it goes in another activity and comes back the same activity where my selectBox implemented but selectBox not shows my previous selected value (it is in the reset state and the business object has that selected value). How to update my selectBox value programmatically? My code is below,

export default function(group, element, translate, dropdownOptions, ddName, _id) {

  if (is(element, 'bpmn:StartEvent') || is(element, 'bpmn:Activity')) {
    var bo = getBusinessObject(element);
    var dropdownBox = entryFactory.selectBox(translate, {
      id: _id,
      label: ddName,
      emptyParameter: false,
      selectOptions: dropdownOptions,
      modelProperty: _id,

      get: function(element, node) {
        return bo;

      set: function setValue(element, values, node) {

        var b_obj = getBusinessObject(element);
        var selectedValues = {};
        selectedValues = values;
        prop[_id] = selectedValues[_id];
        var bo = cmdHelper.updateBusinessObject(element, b_obj, prop);
        return bo;

    if(is(element, 'bpmn:StartEvent')){
      //var selectedValues = {keyValue : attributes[_id]};
      var attributes = bo.$attrs;
      var values = attributes[_id];
      if(values != undefined){
        // Want update my selectBox here 

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