The gemorah in Sanhedrin discusses a hierarchy of batei din when the local beis din is divided or unable/unwilling to paskin on a particular matter. I’m certainly not an expert but I don’t believe there is any formal “appellate process” for a ruling that was already issued by a beis din as there would be in a secular court decision. Thus, a psak din is final unless a clear error is found in the ruling or if new information comes to light. In the latter case, the initial ruling of beis din can be revoked by the originall beis din that issued the psak or by another bies din of greater authority.
