This functionality was added in July 2016. If a “Next Task Date” field is added to a list and a Task is created from within the Outlook Plugin then the Flex “Next Task Date” field will be updated with the date as set. Currently this feature does work if the Task is created from within Flex. This feature enhancement now enables Tasks created from the Outlook Plugin to also update this field.
There is nothing to do for this enhancement. You must have the July 2016 version or later Flex update.