It will be more cooperative if you turn the barrel, just lift the movement retaining ring and some barrel teeth will get exposed.
Looks like the mainspring is broke.You might get by with a quick fix, that is replacing what is broke and faulty or give the movement an overhaul.
Thanks @Nucejoe I've had a little bit of success turning the centre wheel. I've managed to move it on a whole 40 seconds. It does seem to depend on how nicely I ask it to move, it doesn't seem to do it all the time... A rather temperamental old chap it's turning out to be!
Thank you Gaus, the videos are very clear.
Still my problem is more regarding the specific Omega Dynamic case.
Searching more I found some photo of the great site watchguy.co.uk with a similar watch:
I got the inspiration that I can mount the hands before casing the movement.
Still I would like some kind of reassurance that I will be able to fix the outer stem once the movement will be kept in place (i.e. not rotating any more) by the crystal.
I would hate having to pop open the glass from a front access case to start from scratch
YouTube videos can be quite amusing at times and just because they make a video does not mean they actually know what they're doing at all just as a reminder. Then two videos doing a similar thing still does not necessarily make it the right thing.
The first video at 6:23 something is removed from the dial side. Then continuing on in the video isn't that odd there is still a wheel on the other side? The second video is very similar in a way although conveniently we don't get to see a lot because there's a finger in the way in front of the camera though so we don't get see the wheel coming off the dial side it's just mysteriously gone but when he's putting everything in the cleaning machine at 8:46 obviously they both read the same manual or did not read the manual at all is a wild guess there's that same wheel still on the main plate?
Then rather than just give you the answers of why the videos are wrong I'm curious how closely did you follow the videos?