Here's something I learned from a parrotlet forum, used it on our first parrotlets, then used it on all the other birds we've adopted since and it works pretty good.
The way it works is that you train the bird to be gentle on command, they use the command "gentle beak" which I decided to use as well, but it can be a one word command if you don't want to say "gentle beak" to your bird hunderds of times...
What you do is simply touch your bird's beak and say "gentle beak" or whatever word you chose as your command for this, but you touch the beak and say "gentle beak" over and over and eventually the bird will touch you with their beak when you say it. What you do is when you see your bird is planning on biting you, just say "gentle beak" right before the bite and he'll touch you with his beak instead of biting.
This can take a few days with a new baby bird or it can take a few weeks or more, but it will work.
With our first parrotlet, he liked to land on one of us then bite down just enough to break the skin, then he would get mad and growl if you tried to move him or stop the bite, he wasn't biting out of fear but he was more biting because he liked to bite more than anything else. Once I started this training with him it seemed useless because for one I couldn't touch his beak without getting bit, and when I was able to touch his beak he would reply with another bite... this bird was a mini biting machine for sure...
Anyway, finally, after a few weeks, he finally did it, he was on me and went in for a bite and I told him "gentle beak" and he nudged me with his beak and flew off instead of biting me and flying off... Progress... Finally... So now knowing it was working, I kept it up and he eventually grew out of his biting habit but when I saw a bite coming I had a way to stop him.
I got a sun conure next and he wasn't nearly as much of a biter as Blue was, but he had his moments so I used the same training on him and it worked. After that I used it on every new bird we got successfully, then we got another parrotlet...
This guy I wasn't about to give him the chance to bite me like before so as soon as I gained his trust by offering him a treat everytime I passed by him but never tried to touch or handle him, just hand him a treat and let him carry on with whatever he was doing. Once he trusted me I started the "gentle beak" training but this time I was armed with lots of treats...
This time I would touch his beak and say "gentle beak" then hand him a treat, he wasn't touching me with his beak and he had no clue what I was doing but he got a treat everytime he heard this word and I touched his beak.
After a day or 2 of doing this randomly and repeatedly, he touched my finger with his beak... Lots of praise, and a very nice reward was given... This went on for a few days with him touching me with his beak every time I said "gentle beak" and when he tried to bite me, I just said "gentle beak" to him in a soft casual tone (we NEVER yell at our birds, do we?) and he touched my finger with an open beak, so again, lots of praise and a nice reward.
Anyway, try it and work with him on it, you should be able to get him to stop biting this way, just remember, talk to your bird in a soft, casual tone as the more firm or agressive your tone is, they will pick up on it and may bite down because of that instead of just touching you with the beak.
ANY time your bird has a part of your body in his/her mouth, talk softly to him, the gentle tone of your voie alone may be what saves you from a nasty bite.
