There are some sprays on the market which sometimes work, but get one specially for a bird and get a good one.
There could be a multitude of reasons why your parrot has started plucking and although I wish for the best, once they have started it is very hard to cure.
Do you have a friend with another parrot that you could borrow for a few weeks, even a budgie? Sometimes that works but make sure they can not reach each other in case things go wrong.
If the bird is housetrained so it stays at a designated area it may help to make a sort of jungle gym with any old pieces of wood, even firewood will do, doesn't matter what it looks like. Companion parrots all love to climb around and often show off.
Birds are very much creatures of habit and don't like changes so anything to be added to its close proximity should be introduced gradually.