Had round 2 of CoolSculpting on flanks. I experienced a "Thermal Event" on my right flank. Now there's a dark burn mark? (photo)

Very sorry to hear that you had an adverse event. First of all its very rare to have this kind of event so I am not sure if you are going to get a strong recommendation. In my practice I would recommend giving some more time and let the inflammation settle down completely -  avoid sun exposure, SPF and then re-evaluate in 4-6 weeks. Hopefully this will continue to fade. 

I recommend following up with a cosmetic dermatologist for after care and treatment for hyperpigmenatation. This can be improved with a combination of lasers, Aerolase, microneedling/prp, skin lightening, peels, and skin care. Sun protection is essential. 

This discoloration 2 weeks after a "freezer burn" is uncommon. It's probably a bit early to call it PIH (post-inflammatory hyperpigmentation). The most important thing that you can do to minimize long-term darkening of the skin is to avoid the sun and wear sunscreen. A skin care product with 4% hydroquinone like Obagi Clear or Triluma may also be used. If there is pigmentation that remains after a few months, it could be treated with a IPL or other laser or light devices.