Can medication called metanx be used for the treatment of bell's palsy?

Not beneficial. Metanx is a medical food approved for diabetic neuropathy, especially small fibre variant. Beneficial outcomes may take well over 6-9 months. Bell's is an acute event and in most cases, >90%, will recover in a few weeks. It is unknown if those who fail to recover rapidly would benefit.
Metanx. Perhaps it will aid in recovery from bell's palsy but it is not a treatment, per se.