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Can you feel the swelling in the neck- is it hard? If so it's probably an impacted crop- this is serious and the blockage needs to be relieved. I'd certainly advise seeing a vet about it- but you could try syringing a small amount of mineral oil (liquid paraffin) into the bird to try and loosen the blockage.
If the swelling feels soft and movable, then it's probably a ruptured 'clavicular airsac' that is causing the problem- birds don't have lungs like ours, they have lots of air sacs, and if they get a small puncture in them, then the air builds under the skin- this air will need draining by inserting a needle into it- but again it's really a vet job- although any vet could attempt this, not just an avian specialist.
Hope this is of some help