Generate simple workflow like picture below, our human task is parallel approval. Double click on User Task and edit "Data Associations". At the "Output" tab, get the task id and run "getPreviousTaskApprover" function. These steps are: 1 - Create and associate "TaskId" attribute. 2 - Use this formula: "hwf:getPreviousTaskApprover(bpmn:getDataObject('TaskId'))"