Use Apple Watch to breathe mindfully
The Breathe app 
on your Apple Watch encourages you to set aside a few minutes a day to relax and focus on your breathing.
Start a breathe session
Open the Breathe app
on your Apple Watch.Tap Start, inhale slowly as the animation grows, then exhale as it shrinks.
Set the duration of a breathe session
Open the Breathe app
on your Apple Watch.Turn the Digital Crown to increase the duration.
You can choose a time between one and five minutes.
To set this as your default duration, open the Settings app
on your Apple Watch, tap Breathe, then turn on Use Previous Duration.
Adjust breathe settings
You can change how frequently you get breathe reminders, mute breathe reminders for the day, change your breathe rate, and choose haptics settings.
Open the Settings app on your Apple Watch, tap Breathe, then do the following:
Set breathe reminders: Tap Breathe Reminders.
Mute breathe reminders: Turn on “Mute for today.”
Change your breathing rate: Tap Breathe Rate to change the number of breaths per minute.
Choose haptics settings: Tap Haptics, then choose None, Minimal, or Prominent.
You can also open the Apple Watch app on your iPhone, tap My Watch, tap Breathe, then adjust a setting.
See your heart rate during breathe sessions
Open the Health app on your iPhone.
Tap Browse, tap Heart, then tap Heart Rate.
Tap Show More Heart Rate Data, swipe up, then tap Breathe.
Use the Breathe watch face
Add the Breathe watch face to get quick access to breathe sessions.
With the current watch face showing, touch and hold the display.
Swipe left all the way to the end, then tap the New button (+).
Turn the Digital Crown to select Breathe, then tap to add it.
Tap the watch face to begin a breathe session.