More bathes. A change in diet. Full spectrum lighting. More bathes. Foraging opportunities. Trick training. More toys. More foraging opportunities. Have I mentioned bathes?
Birds typically don't pluck when they are soaking wet and if his feathers are bothering him, it may help to give him more frequent bathes.
If he's not on a healthy diet, it could lead to dry, itchy skin. A healthy diet may help that.
Foraging is a great way to keep a bird busy. Birds don't have food bowls out in the wild. They have to forage for their food and it can take hours to get enough food to satisfy them until the next time they go out to eat. Our pet birds can spend 5 minutes at the food dish and be done. They are now finished eating for a bit, so what are they supposed to do next?
Is your conure flighted? Flying could also be another great way to stimulate your bird! Teach him to fly to various stations around the house, then recall him back to you!