The calendar and your days
Running on a rest day
On the calendar, today's rest day has Run, which starts an easy run at once, and every rest day has Add, which adds a workout of your own to that day.
On a rest day or a strength day, today's workout screen offers Start a free run, and the watch offers FREE RUN: an easy run with no distance or targets.
A run on a day with no planned run makes up a run you missed earlier that week, or counts as a bonus run.