Dave and I have always done this as a "habit" with our birds. We do this mostly with just our macaws because they tend to reject touch more than our other parrots, such as our cockatoos or grey. So, to be on the safe side and to always know that we won't be getting bit in the face, we make sure to present a treat when we kiss our birds on the top of their heads.
This eventually can be phased out to include all touch, even just a little pat on the head.
To encourage your bird to better accept being pet, present them with a treat so that both petting and treating are happening at the same time. The treat is presented and given first so it is taken and consumed by the bird at the time as being touched. You can then present a second treat as a reward for allowing you to touch him.
Your bird cannot bite you AND take the treat and eat it at the same time; this is called incompatible behavior. Not only are you avoiding a possible bite, but in this process you are pairing something positive (a treat) with touch. This goes a long way if you make this a habit too. Your bird will actually look forward to the touch and will not require a treat every time.
Jamieleigh Womach has been working with parrots and toucans since the age of 17. She isn’t homeless but is home less than she prefers to be. She travels the world with her husband, daughter, and a flockful of parrots whom she shares the stage with.