I have had a lot of birds over the years. Bought a Sulphur crested cockatoo that was very scared of hands. I taught him to step up on a short perch held in my hand , which was covered by a towel. He was not a biter, but was fearful. Always move slow when training birds. They see fast movement as a threat. The conure can bite the stick and not hurt you, which is why it is such a great tool. Once you teach the bird to step up, walk around slowly with the bird on the stick. He will get used to it and start to feel more trusting of you. If you fill the seed and water cups before you uncover the cage, the bird may not try to bother you. After a while, i slowly started using a smaller towel until the bird could see my arms . Talk calmly to the bird as you work with it. After a while, i would grasp each end of the stick with a hand. As the bird got used to that, i would move my hand towards the middle of the stick. After a while there was very little stick for the bird to step on. He stepped on my hand. Didn't freak out. Keep talking. Eventually the bird learns to step up on command and will step on your hand from the stick (which is handy when they are up on a curtain rod) or even directly on your hand. This Cockatoo learned to trust me, and in time let me pet his head on the bare spot under his crest and the place where the body meets the wings... with my bare hands. The fellow that owned the bird spent a lot of time away from home and did not cage the bird. So i suspect the bird chewed furniture. They love wood. I think the guy would swing at the birds with his hands when he came home and discovered damage. The conures we have had were more screamers that biters. They can be very loud. Which i suspect is why you see so many conures flying loose in Florida.
I hope some of my tips will help you. If you need to rehome the bird, you might consider placing it with a breeder where they can live in large flight cages with another bird.