Is there any remedy for an underdeveloped right palm?

I take it that only one hand is affected (probably left). It is first imperative that one finds out the reason for this discrepancy. If the cause is treatable like a tumour somewhere in the wrist or forearm region, then it is receptive to treatment. Having said that, it is impossible to comment specifically without assessing the boy as a whole. I would recommend assessment by a pediatric neurologist first.