TRX350FM2, seized rear brake drum

First posting on this forum.
Rear brake drum is seized after ATV was allowed to setup subsequent to wet ride. ATV is on Jack stands. Front axle turns but rear axle will not turn (even slightly) if I try to rotate the left side tire. Have removed tire/wheel and hub plus disconnected both cables and moved lever to full open position. Lever is not free but can be moved back and forth by tapping with mallet. Tapping drum has had no effect.