In theWatchapp, selectMindfulness.
Under theMindfulness Remindersheading, tap the two toggle switches next toStart of DayandEnd of Daytooff/white.
Alternatively, selectNotifications Offin the area above this section.

Can I Customize My Breathe Reminders?
What Triggers the Breathe Notification on Apple Watch?
The Breathe app reminds you to take a break every four hours by default.

The Mindfulness app scales it back a little and prompts you at the start and end of each day.
How Do I Turn Off Breathe Reminders?
you’re free to turn off reminders for Breathe and Mindfulness through theWatchapp on your iPhone.

Still, it’s easier to eliminate or mute notifications if you think you might use them someday.
FAQ
It depends.
It’s not possible to delete such apps in older versions of watchOS.

Toturn off Power Reserve on an Apple Watch, tap the battery indicator on your Apple Watch face.
Drag thePower Reserveslider from left to right, then tapProceed.