Oppo Watch Faq page 23

Press and hold it for 1.5 seconds to wake up the Google
Assistant.
2.5 What can the "Multifunction" button
do？
l Power on: Press and hold it for 2 seconds until the "OPPO"
logo appears.
l Power off: Press and hold it for 1.5 seconds and drag the
"Power Off" slider to the right.
l Force restart: Press and hold it for 12 seconds.
l Turn on "Power Saver"：Press and hold it for 1.5 seconds
and drag the "Power Saver" slider to the right.
l Press once to call up the app assigned to this button.
2.6 How to assign an app to the
"Multifunction" button？
On your watch, you can go to "Settings > Personalization >
Customize hardware buttons" to assign an app to this button.