Any task on today's list can be rescheduled directly from the watch without opening the iPhone SAU App.
Rescheduling a task in SAU on Apple Watch
To do this, select the task in the list, tap on it, and select one of the two options to reschedule it - "For tomorrow" or "In 7 days". The task will then disappear from the list on the watch, as it only shows today's tasks.