//Sendback an activity instance to previous step

IWorkflowService wfService = new WorkflowService();

var wfResult = wfService.CreateRunner("20", "Alice")

.UseApp("DS-100", "Book-Order", "DS-100-LX")

.UseProcess("PriceProcessCode")

.PrevStepInt()

.OnTask(id) //TaskID

.SendBack();