function onHoldAction() {

var tableName = 'incident'; //table name here
    var sysid = g_form.getUniqueValue();
    //Create and open the dialog form
    var dialog = new GlideDialogForm('ON Hold', 'incident'); //Provide dialog title and table name
    dialog.setSysID(sysid); //Pass in sys_id to edit existing record, -1 to create new record
    dialog.addParm('sysparm_view', 'on_hold_dialog_view'); //Add view of the form
  dialog.addParm('sysparm_hideButtons', 'true');
    dialog.setLoadCallback(function(iframeDoc) {

        // To get the iframe: document.defaultView in non-IE, document.parentWindow in IE
        var dialogFrame = 'defaultView' in iframeDoc ? iframeDoc.defaultView : iframeDoc.parentWindow;
        dialogFrame.g_form.setValue('hold_reason', g_form.getValue('hold_reason'));
        dialogFrame.g_form.setMandatory('hold_reason', true);
        dialogFrame = null;
       
    });
    dialog.render(); //Open the dialog
}
Tried this.
But still seeing the UI action