Since you have to ask how to remove the case back, it might be best if you don't try to open it. The case back is not removable. If it needs work, it needs expert attention. You may well have a caliber 550 movement in your watch, a picture of which you may see in this link to Dr. Roland Ranfft's movement archive.
http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2uswk&Omega_550
It's too nice a watch to use to experiment on!
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