So I had this issue with Kospet Optimus Pro not turning on and here’s my recount on the “fix” in case somebody faces a similar issue.
If I tried charging it, the display would turn on briefly to reveal for a few seconds that the battery was charging, but then it would turn off, and pressing power button did nothing. Ultimately I opened up the lid and slid a thin blade in between the power button and the area underneath that it was supposed to be pressing. The watch turned on and I realized that after about a year of use the power button became somehow short of reaching that space underneath. I ended up shoving small bits of napkin tissue in between and screwing the lid back on, so the power button became effectively functional again and I regained the ability to turn it on.
Hope it helps someone some day.