code

if (entityiterator != null && !entityiterator.level().isClientSide()) {

   ResourceKey<Level> dimensionKey = ResourceKey.create(
       Registries.DIMENSION,
       ResourceLocation.fromNamespaceAndPath("nextlevel", "pocket_dimension")
   );

   ServerLevel targetLevel = entityiterator.getServer().getLevel(dimensionKey);

   if (targetLevel != null) {
       entityiterator.teleportTo(
           targetLevel,
           entityiterator.getX(),
           entityiterator.getY(),
           entityiterator.getZ(),
           java.util.Set.of(),
           entityiterator.getYRot(),
           entityiterator.getXRot(),
           false
       );
   }
}