about the mutilple instance

I use the bonita studio 7.0.1 When it comes to the mulitple instance regarding to the task, I go to the general -->iteration and I find the "Iterator" field is disabled and I couldn't input or change anything in this field. It takes me a while to get aware of this field use the variable called "multiInstanceIterator", but I couldn't get this kind of variable in the actor filter even I call the API processAPI.getProcessDataInstance("multiInstanceIterator",getExecutionContext().getProcessInstanceId()).getValue()), I found something very interstring , this variable could be found and used in the connector. So the background is that I generate the muliti instance from the list (list of bonita user id)and I'd like to use this kind of variable to set the different assignee in the actor filter since this task is for consign. How can I achive it ? Thanks in advance.