In the Gantt view in Orchestrate, planners are able to unplan tasks by right clicking and selecting "Unplan tasks". This option doesn't appear in the work list view.
The functionality to unplan tasks from the work list view is different to the Gantt Chart view:
Click Work List or Agenda from the plan
Open the Task Planner
Select your task in the Work List / Agenda view (or you can select multiple tasks from the Work List / Agenda by holding the CTRL or SHIFT key)
Click unplan from the Task Planner
