After I accepted the mission from Q, it isn’t listed as option when I talk to him again, which means you already have it. Did you tried going to your In Progress mission list? Default key is “J” –> In Progress. Find Omega Molecule Stabilization (Daily) missions listed under Events. For me, it is in same section with Dilithium Mining Daily, Tholian Red Alert, etc. You should be able to make it as primary mission there. If this doesn’t work, report a bug.