To reset the start date without changing the due date, enter None in the Start date box, and then press ENTER. Click in the Start date box again, and then enter the new start date.
Note If you set the due date to a day of the week that is outside the normal recurrence pattern for the task (for example, the date you set falls on a Wednesday, and the task normally repeats every Tuesday), you will see a new task in the task list for this one-time exception. The new task won't repeat, but the original task will continue to repeat as set.