Omega pocket watch

No such part as a “mainspring wheel”. You might be referring to the “ratchet wheel” as pictured at A. That screw is usually a right hand thread. However, if you refer to the crown wheel at B, that screw is often a left hand thread. It depends on the particular watch. In the image, A is the ratchet wheel, and B is the crown wheel. The watch in the image an a U S made Elgin. The screw at A is a right hand thread. The one at B is a LEFT hand thread. Without your having told us which particular Omega you are dealing with, I suspect the two screws will be like the example I’ve shown. But on the odd occasion, with U S made watches, the screw at B is also a right hand thread.