What are your concerns about letting him out?
My birds are "no touch" and I was definitely apprehensive about letting them out of their cage. What would happen if they went someplace that was dangerous to them? Or, really, how would I get them back in if they didn't want to, or couldn't figure out how to get back into their cage?
First, take a look at the space where you would be letting the bird out. Is it bird safe? Are there plenty of perches that the bird would give the opportunity to stop and rest somewhere out of the way? Is it secure so that he can't get out into other parts of the house and/or no one's going to be opening a door at just the wrong time?
If you've got a safe space for him to fly, I'd start by setting up a perch inside and outside the cage to make it easy for him to see how he can get out and then get back into the cage when he wants to. Then, I'd pick a day that will be quiet and you can simply let him come out of the cage when he's ready. I made sure to leave the food and water in the cage so I knew my birds would go in eventually. And then we just hung out. Honestly, the first few days even if they came out they mostly hung out on the highest corner perch they could find, but the important thing was that they were getting accustomed to getting out of their cage and had more room to use their wings.
Since it sounds like your bird already knows something about this, he might find this all pretty easy. I'll admit that Esme used to get lost and didn't know how to get back into her cage - fortunately, Mustrum would go down to the entrance and wave her in. That was probably the biggest problem we had and I mostly solved it by stringing a rope from across the space so she could fly to the rope and then walk down the rope into the cage.
For me, the important thing was having a safe space so that I knew I could simply wait them out and I didn't have to worry about trying to catch them.