I think you need to take a few steps back and give your conure some time and space, and avoid all biting situations.
When you want to change your conures food and water, lure them with a treat and put it somewhere else in the cage so they are distracted from being territorial.
Kiwi rarely bites me now, but sometimes when she is cranky or, sometimes when I wear something like a cap or beanie, she will think I'm some scary monster and will bite out of fear, and also territory when I touch her food dish. I'd step back, give her some time to recognize I'm not a threat, then she's okay.
What is your conure's diet? how much sleep and sunlight is he getting? Does he have a big enough cage? Lots of toys and foraging toys? Lots of time outside the cage?
All that plays a part in his behavior, and it doesn't take a parrot trainer to tell you that. Try think of how you feel when you don't have enough sleep or have had a bad meal, and this big hand comes down and starts moving you around and trying to take your delicious food away.. you just might bite too!!