How to season a giant cast iron cider press?
I would not heat up a large cast iron press - too much to go wrong there, little benefit. You are not frying on the thing.

Clean any oil/rust that's on it, dry carefully, oil it with mineral oil or wax it with beeswax (or paraffin wax, but beeswax will probably stick better,) use it, clean it up well, dry very carefully, and re-oil/wax before storage.