Botulinum toxin injection to masseter will relax the muscle, reduce the excessive activity and spasticity and treat Bruxism. Eventually and after a long time to my experience, the muscle will get smaller. In my opinion it is best if you visit a plastic surgeon for a consultation to analyze your face and discuss the possible options for fillers, fat grafting to rebuild the foundation lost by age, do some countering of the face and at last do the small details. Keep in mind that there is no quick fix and that multiple sessions are advisable. Dr Tarek