Potty training is dangerous for birds. Birds are not mammals. Their bodies are designed to release waste very, very regularly to keep their bodies light enough to fly. Indeed, a flighted bird often poos just before they take off because even a gram or less makes a difference. They are not like a dog who only needs to defecate and urine a few times a day, and who you can train to go outside.
Training a bird to release waste on command by using a prompt word is again very dangerous. You risk your bird holding it in until they hear the prompt word, and not pooing unless they do. Their bodies are simply not designed to hold onto waste. There are horror stories of birds learning to hold their waste until they hear the prompt word, the prompt word not being given for whatever reason, and causing all sorts of physical problems as a result.
I have come to an understanding with my girl where she mostly doesn't poo on me but can poo anywhere else she likes. I can feel her do a little shuffle just before she poos, and when she does this I ask her to step up, put her somewhere else, and say "thank you!" when she does poo. No rewards, no treats, not even the usual word I use to praise her when training. I try to keep the two (toileting and training) as separate as possible.
If she does poo on me, no big deal. It's just a bonus if she doesn't. I provide some perches that she hangs out on when she's out of the cage and make sure that the surface under them can be easily cleaned, and I keep a spray bottle of Poop-Off and some kitchen towels to hand.