I would also say that is not a good method for building trust. It sounds like flooding, a method for overwhelming the bird until they give in and accept a negative stimulus. It is a type of prolonged exposure therapy, used to force the animal (or person) to confront the thing that they fear for a long period of time.
Some people advocate flooding because it can produce fast results. But it is traumatic and can result in the animal developing learned helplessness, rather than true healing of the underlying trauma that caused the fear. This can result in unpredictable problems later on, when the same issues start to appear under new circumstances, because the fear is unresolved. Or the therapy might fail completely and the animal might become sensitized - instead of being less reactive to the negative stimulus, the new trauma causes even greater fear and more extreme avoidance behaviors.
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Imagine if you have an irrational fear of spiders, so your therapist decides you need to confront your fear head on. He locks you in a dark basement room full of spiders and cobwebs for an unknown length of time. You are terrified and want to escape, but you can't leave. You scream for help, but no one lets you out. You see a big spider, watching you from the corner of the room and you feel paralyzed with fear. Suddenly, something brushes against the back of your neck and you completely lose it.
A few hours later, you are emotionally drained and physically exhausted, unable to scream or thrash around, just laying on the floor, blankly staring at the dusty cobwebs on the ceiling. You don't even react when a fat black spider crawls across the bare skin of your arm.
Are you cured? Maybe. After this experience, I imagine encountering a harmless jumping spider in your kitchen would feel pretty tame. Or maybe seeing that spider will trigger a flashback to this basement room and you will be even more scared. It could go either way, really. And that's the problem with flooding. It can work okay for overcoming mild fears, but if your fear is too strong, direct confrontation is quite traumatic. And new trauma doesn't fix old trauma. It just adds to it. Like another layer of dust on the cobwebs.
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Long story short, I would recommend patience and gentle handling as the better approach for overcoming fear and building trust.
For your bird, I would try bird-proofing the entire room and clearing your schedule before letting the bird out again. Pick a time in the afternoon or evening when you don't have any other plans or anywhere you need to be for the rest of the day. Then let the bird out and allow him to explore without a lot of direct interaction. Stay in the room to monitor, but let him do what he wants with his freedom. That might mean he spends a few hours up on the curtains and that is fine. Keep yourself entertained with a book or whatever. Maybe play some relaxing music. Keep an eye on the bird, but pretend to "ignore" him rather than just watching constantly so he doesn't feel hunted. It might take several sessions, but he should eventually start to relax and explore other spots in the room. It helps to offer safe landing spots, like a perch on the outside of the cage or a play gym/tree in a nice location. Higher locations will feel safer, so provide some nice landing spots up high ... or expect Charlie to find his own.
To get him back to the cage without problems, there are several different approaches. He might go back on his own when he gets hungry or when it gets dark out. Placing a nightlight by the cage and dimming the room lights might encourage him to return once it get late.
If he is reluctant to return, you can try offering a perch and transporting him there, like you did with the food dish.
For a more hands-off approach, you could gently herd him back to the cage by walking slowly over to his current location and allowing him to relocate to a different spot. Captive birds usually see their cage as a safe haven, so he will likely return there eventually, given the choice.
If all else fails, you might allow him to remain out of cage for the night, assuming the room is completely bird-safe and you don't have other animals or birds that might hurt him.
The goal is for Charlie to be able to be let out and put back easily, but it can take a while to reach that point, especially with an untamed bird. Keep working on building trust and target training. Step-up is a very useful trick for getting birds to go where you want.