I can do nothing with the watch now. Can't back up cause it doesn't connect to my phone. I will rest it till next week. If it still refuse to wake up, I will need to bring it to svc centre. I've tried every way I can find from youtube/Google but.. they all just doesn't work
Might be software issue, you may go to the nearest Samsung Centre and get your Galaxy Watch4 diagnosed.
Appointment can be booked at the Support tab in this Samsung Members app.