If you want to avoid surgery there are temporary alternatives in the form of Dysport or Botox.  Either can work to temporarily relax the muscles pulling the brow down.  Just keep in mind that you’ll have to continue treatments indefinitely, as well as incur new costs with each new treatment.

For a permanent solution surgery may be the only option.  A brow lift can be tailored to an individual’s specific needs by lifting one side more than the other and this can help brow symmetry a great deal.  I’d recommend an exam with a Board Certified plastic surgeon experienced in situations of brow asymmetry to better assess your needs.  You can then decide on the least invasive course of treatment that will yield the best results.