Ok, I am really pissed off. Someone posted an interesting question (don't remember who but you know who you are) about getting a clipped parrot flying again. I spent a long time writing a thorough answer and then when I hit submit the question disappeared and I couldn't even go back to retrieve the answer I wrote because it said topic doesn't exist any more. Finally I had to hack the forum for a moment to spit out what I put in so that I could get my answer posted.
This is a two part question. Part I is about physiology and part II is about psychology. There are things we can do to improve each of these but there is only so much we can do.
Firstly the parrot needs to grow back its feathers which in itself is a challenge. Kili used to be clipped, grew back some feathers but broke others. Right now she's down to just a single primary on one of her wings because every single other primary feather broke. She can barely fly any more. I'm worried they will start breaking again when they grow back without the protection of additional feathers.
Next there could be muscle atrophy, this will be exercised gradually over time as you work on the psychological exercises. The parrot naturally doesn't want to fly as it has learned to live without flight through habit over all this time. What you will need to do is start out by developing motivation and training routine (if you haven't already). Start with basic target training. Next buy my parrot training stands. Sorry the website is still incomplete but they are available. You don't have to buy them but honestly this is what I used and think it's the absolute best tool for the job but you can try using some chair backs or play gym if you'd like. The beautiful thing about the stands is that the height is adjustable and they can be positioned at progressively further distances.
Teach the parrot to walk from stand to stand by targeting back and forth for treats. Progressively increase the distance. Eventually it will get large enough that the parrot will refuse to come. Make it back a little closer. Keep going back and forth (remember this can take minutes, days, or months before you see results). Eventually the parrot will slip as it's going across the almost impossible to walk over gap and it will reflexively flap to get back up. This is when the real learning begins. You cannot force this. The parrot has to come to this conclusion itself. Keep going and the parrot will start to learn to flap as it's going across and now when you increase the distance some more it will hop and fly. This will become both psychological and physiological exercise. This can take a very long time but slowly the parrot will build up muscle and confidence. The beautiful thing is that you can soon convert this to recall and since the parrot is not previously flighted, it can learn to fly to you before anything else. You have the opportunity to shape where your parrot will choose to fly to. By making it a habit of putting on certain places and having it fly to certain places, it will mostly stick to flying to just those and not others in the long run. Here are articles I wrote about doing this process with my parrots:
http://theparrotforum.com/viewtopic.php?f=15&t=228
http://trainedparrot.com/index.php?bid= ... +to+Truman