Thanx a lot dr. Sassi!
I tried same steps and got rid of this little tilt among all objects. This was the real aim.
Altho, once you create new null by itself it is in centre and when your move all children under new null they stil be way off the centre. I selected all children and then created new parent /null) for them (opt+g), then created new null to centre, moved all children to new null (on the centre) and copied coordinates of previously created parent null to new null. Then zeroed all cordinates of the new null. That fixed parent tilt. Altho... for some unknown reason position of the new null is not exactly the same as created group null... but this on I will figure aout myself. Thanx once again!

Thank you for your quick answer!
I do not need to rotate the whole object. I need to reposition and rrotate some objects. If their rotation is slightly off (approx. 9.6355 °), then it is quit unpleasant task.
I tried your second suggestion... but maybe I misunderstood something.
I uploaded stp and c4d models here. Those are not very large - CD file is about 50 megs. Step file is about 150 megs.
https://www.dropbox.com/scl/fo/ssh8yag8xs9v3bspuinpy/h?rlkey=55q11a4a9lqvzy3v6i9y9ntgg&dl=0
I would really appreciate if you could take a quick look.
Thnx!

It might be kinda newbie problem...
I have stp model with about 1400 objects in it. All objects (which form one larger machine) are heavily ofo their axis center. Fixing axis center is easy, but all objects rotation is also off. Is there a way to fix all objects rotation at once without breaking their actual position and rotation? Tnx in advance!
Screenshot here https://www.dropbox.com/scl/fi/fjduqdrl133f07bfdnb7j/screenshot.jpg?rlkey=f77fodcgd7fy633s8d53dvc4a&dl=0