This technique shared by [Andy Kong] is for 3D printed lenses, but would probably be worth a shot for any resin prints that need to be made nice and clear. The link to his post on X is here ...

Pretty soon he was using silicone rubber to make two-piece, high-quality molds of lenses, good enough to try a few casting shots with epoxy resin. [Zach] ran into a few problems along the way ...