It's possible it's to do with some configuration on the watch itself that's causing bluetooth to be disabled. Please can you try the steps here and see what happens?
After that, you should hopefully be able to connect (it ensures it ignores any config that was previously on the watch). After that, maybe try upgrading the firmware via the 'firmware update' app.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
It's possible it's to do with some configuration on the watch itself that's causing bluetooth to be disabled. Please can you try the steps here and see what happens?
https://www.espruino.com/Bangle.js2#resetting-without-loading-any-code
After that, you should hopefully be able to connect (it ensures it ignores any config that was previously on the watch). After that, maybe try upgrading the firmware via the 'firmware update' app.
If all that fails, you could also try uploading firmware using the NRF Toolbox app: https://www.espruino.com/Bangle.js2#android-ios-app but I'd say try that only as a last resort