Bowen Therapy sounds a lot like Active Release Technique and/or Myofacial Release.

Both can be helpful for the muscle spasming and head aches and such that result. There may be some improved blood flow from these treatments that can lessen the cognitive PCS symptoms.

Some articles suggest Bowen Therapy has resulted in full recovery from PCS. I would suggest being very cautious about thinking it can resolve all of the PCS symptoms. A concussed brain will still be sensitive to future impacts with the risk of even longer term symptoms.