Simply press the button of BPM Connect once to turn it on. Press and hold the button of BPM Connect for 5 seconds to turn it off.
Note: If BPM Connect has not been installed yet, press and hold the button to turn it on.
https://support.withings.com/hc/en-us/sections/6215752935825-BPM-Connect
https://support.withings.com/hc/en-us/sections/360003813073-Tutorials