how to show selected values in multi-select - laravel

Question

I'm facing one issue about multi-select.
onchange i'm runnig ajax and on ajax success option appends to multiselect.
but at the time of edit i'm not able to trigger ajax and not able to show selected option in multiselect.
please check my code
form fleds
<div class="form-group {{ $errors->first('preferred_city', 'has-error') }}">
<label class="control-label col-lg-2">Preferred City
: </label>
<div class="col-lg-10">
<select name="preferred_city[]" class="form-control" id="preferred_city" multiple="multiple" style="color: #333">
#foreach($cities as $preferred_city)
#if(!empty($studentsDetails->preferred_city))
<option value="{{$preferred_city->id}}" {{ (in_array($preferred_city->id,\GuzzleHttp\json_decode($studentsDetails->preferred_city) )) ? 'selected' : '' }}>{{$preferred_city->city_name}}</option>
#else
<option value="{{$preferred_city->id}}">{{$preferred_city->city_name}}</option>
#endif
#endforeach
</select>
<span class="help-block">{{ $errors->first('preferred_city', ':message') }}</span>
</div>
</div>
<div class="form-group {{ $errors->first('collage_preferences', 'has-error') }}">
<label class="control-label col-lg-2">College Preferences
: </label>
<div class="col-lg-10">
<select id="collage_preferences" name="collage_preferences[]" class="form-control" multiple="multiple">
</select>
<span class="help-block">{{ $errors->first('collage_preferences', ':message') }}</span>
</div>
</div>
js
collage id's i'm fetching from database
var collage_pref = {!! $studentsDetails->collage_preferences !!}
I'm triggering preferred_city on page load
$(document).ready(function(){
if(studentsDetails !=null){
$('#preferred_city').trigger('change');
// $('#pic_file').trigger('change');
}
});
$('#preferred_city').on('change',function(){
$("#collage_preferences").multiselect('rebuild');
$.ajax({
url:'{{route('student.getInstituteslists')}}',
type:'get',
async: false,
data:{grad_course:$('#grad_course').val(),preferred_city:$('#preferred_city').val()},
success:function(e){
$('#collage_preferences').multiselect('refresh');
e.forEach(function(inst){
var data = '';
data +='<option value="'+ inst.id+'" >'+ inst.institute_name+'</option>';
$('#collage_preferences').append(data);
});
$('.collage_preferences').multiselect('rebuild');
}
});
});

Answer 1

$data = [];
$data['airlines'] = '';
$airlines = (Airline::select('Code','Name')->get())->toArray();
$myairlines = BlackoutAirline::where('SupplierId',$request->SupplierId)->pluck('AirlineCode')->toArray();
foreach($airlines as $airline) {
if(in_array($airline['Code'], $myairlines) ){
$data['airlines'] .= '<option value="'.$airline['Code'].'" selected>'.$airline['Name'].'</option>';
}
else{
$data['airlines'] .= '<option value="'.$airline['Code'].'">'.$airline['Name'].'</option>';
}
}
return json_encode($data);