Ok maybe I'm weak or maube it's hard the first time but I can't unscrew the lens that is supposed to be exchangeable...

Is it just me?

Nope, its not you... its on there super tight.  I had to go get a rubber jar opener and use that on the lens cover and turn it counter clockwise, and then I was able to get it off... Also, be leery of the rubber gasket when you take it off... it may become unseated from where it is supposed to sit and if its not sitting right and you put the lens cover back on and put it in the water, you run the risk of having water or some form of condensation occur on the inside of the lens cover.  This happened to me yesterday, and I had to take the lens cover off, clean the lens and then use a toothpick to channel the rubber gasket into its crevice on the OA itself.  Then I tested again and it worked fine... no water or condensation got inside.

Hi, we're sorry for the inconvenience. In order to achieve the purpose of waterproofing, the filter is really tight, it is not easy to screw it down. It is recommended using the cloth pad then rotate the filter counterclockwise, do not press the lens glass to avoid damage. Please keep us posted on the latest progress.

OKAY!   How am I suppose to know this thread is about the Osmo Action?   I only know it because the "hard to remove filter cover" has cropped up in the last few days in the Subforum that applied to the Action Camera.  But it is lost in a meaningless morass of every OSMO thread.  Please restore some order to subproduct threads.  This really is impossible.