If you really want to open it yourself, try using a rubber ball. It works in most cases and you can be sure not to damage the back.
Tutorial video:
https://www.youtube.com/watch?v=vNHPstmjVNsBe careful when screwing the back in. Put it horizontally, adjust the rubber gasket, rotate a bit clockwise for screw to adjust and then rotate clockwise with fingers and tighten with ball.
Disclaimer: I'm not a watchmaker and not an expert on watch opening and have never opened one of my expensive watches, I leave that to my watch maker. But if I had no option, I would use the rubber ball.