So while I have not dealt indian ring-necks before, I have had several cockatiels with very similar behavioral problems. First I try to figure out the bird's favorite treats. I leave several humble offerings in his foodbowl and see what it prefers. Usually my birds tend to be crazy about millet or corn, two things i normally don't give them on a regular basis except as treats. I like using millet as it offers significant distance betwen my hand + the bird.
Then for a good month or so, I slowly approach the cage, stopping whenever the bird appears alarmed (probably much easier to do w cockatiels considering their crest) and trying to talk very calmly until the bird calms down again. When I reach the cage, I show the bird the treat and offer it in the foodbowl. I stay around a little, sometimes pretend not to watch him/take a nap/etc, and see if he takes the treat. If he doesn't take the treat, take back the treat and try again in an hour. I rinse and repeat this a few times daily to make his association with me more positive. Hopefully with repetition, your bird will go towards the treat faster as a sign that he is familiar with the routine and you.
Then if you can get that far, I would suggest opening the cage door and placing the treat near the door. If you have a mounted cage set-up or something, I like placing a ladder around the door and putting the food there. Just make sure it's secure because birds sometimes startle themselves when they move their food lol. Just remember if the bird doesn't take the treat, just take it back, and come back in an hour (and maybe leave the door open if you can keep an eye on it, no need to startle them with door opening/closing all the time). It makes them curious.
I find a lot of my birds love to pretend they don't care but they are secretly curious if you take away the offering and put it back later and wait.
Then I start offering them millet/some form of treat held far from my hand from the cage door. I don't like sticking my hand in their cage as it is their territory. They are much more willing to interact with you outside of you invading their safe space. From then on you try to get closer and closer with hand feeding bribes and work from there. I also recommend trying step-up on a ladder first rather than a hand. It's just a lot of slow progress. Sometimes they make leaps, then just go back to not making that leap a day later.
I feel the most common mistake I used to make when I first dealt with birds is trying to offer a bird a treat from my hand right away, especially when they are very skittish and untame. I'm a bit against pushing a scared bird, it has never worked for me to force a bird to do something it does not want to do.