sorry i don't fully understand your problem

<div class="col-sm-3">
    <div class="form-group"> <label><?= e(trans('mavitm.restful::lang.backend.request_type')) ?></label> 
        <select name="config_data[request_type]" class="form-control custom-select">
            <option value="">--</option>
            <option value="get" <?=($formModel->config_data['request_type'] == "get" ? 'selected':'');?>>GET</option>
            <option value="post" <?=($formModel->config_data['request_type'] == "post" ? 'selected':'');?>>POST</option>
            <option value="all" <?=($formModel->config_data['request_type'] == "all" ? 'selected':'');?>>All</option>
        </select> 
    </div>
</div>