Only Project Managers and Administrators can reopen a completed task or perform limited actions on them.
To reopen a completed task, the Project Manager or Administrator must first set the status filter setting in a task list to “All Completed Statuses” for the task to be listed. The completed task’s status can then be changed to a “Waiting” or an “In Progress” status directly from the task list using the “Actions on checked tasks”. Thereafter, the task will once again show up in user lists as an incomplete task and will be editable by any Normal user with sufficient project level rights.