You might have better luck trying under the bird behavior or training forums.
I don't know that much about ringnecks but it seems like a certain percentage of them are naturally shy and nervous even when handfed and treated the same as their siblings. It might be an adaptation in the wild (where a few birds may serve as flock lookouts). Do you know if he was tamer at one time or if he's always been like this? Either way you should be able to train him, but if he was a previously tame bird who just hasn't gotten much attention lately, he will tame up again much easier than if he was never tame.
Either way, I would take the time to observe him, and find out how close you can get to the cage without making him nervous. Put a chair there and spend some time sitting there, reading or otherwise ignoring him, just to get him used to your presence. When he seems relaxed (for example if he fluffs or stretches or starts to preen), you can go over and drop a piece of apple into his dish, without looking directly at him, then go back to the chair and ignore him again. Hopefully he will eat in your presence, if he doesn't, you might need to move a little farther away after offering the treat, but I would still stay in the room.
As he becomes more relaxed with you, you can inch that chair closer to his cage - it might take days or it might take months depending on how scared he is - but once he seems calm with you right next to the cage, you can start trying to offer him the apple by hand and actually work on training and interacting with him more.
