Bangle 2 button not working properly -> disassembly?

No problem - I think the main post you're looking for is http://forum.espruino.com/conversations/372404

When i do this to replace phone screens, i use about 80 degree hot air. What is the recommended temperature for the watch that will not harm the case?

The case is ABS plastic so realistically as long as you're below 100 degrees C there's no real chance of damage (ABS usually melts as you get near 200 C)

edit: I just tried here with a dead one, being very liberal with the heat (heat gun set to 130'C), and the case was fine but the LCD wasn't. The datasheet for the LCD lists max 80 degrees C storage temp, or 70 degrees when working - so I would heat the glass up slowly, and try not to get much past 80.

The big issue is getting the LCD 'started' - because the plastic goes around the glass there's no way to get under the edge, so you need to use a suction cup.

But it might just be worth me sending you out a replacement...