Goto petsupermarket and get one of their harnesses, they are $11 to $17 depending on size. Let him play with the leash part like a toy, it's cheap he can destroy it if he wants. The harness from petsupermarket has three clips on it and it is easier to put on since it doesn't have to slide over the face and head nor do you have to pull his wings through the loops and then adjust the whole thing. Once he is comfortable with this cheaper not as safe harness you can start to work with the aviator.
In other words the cheap one from petsupermarket is a great "training harness" but not safe for regular use. I've had Mojo (B&G) for two weeks and he has had this harness on 4 times, soon I will order an aviator.
Take it slow, here is what I did.
Let the bird touch it with his beak and feet.
Play with the harness, wrap it around your hand while you watch TV where he can see you.
Touch him while the harness is on your hand or arm.
Touch his wing with the harness
Probably the most difficult part is touch his back with the harness.
When you attempt to put it on for the first time, have the bird in your lap instead of a perch or his cage.
