That is really great work with the harness!. I suggest you do that for 5-7 days, and theen see if you can drape the harness over his body while his head is in the loop. Adjust it to be loose fit and daily adjust a tiny bit more tighter, so the final fit is confortable over his wings. This not the same as fitting his wings into the loops - that comes later. This excercise gets him used to the weight and feel of the harness.
Develope specific verbal and hand signals for putting it on and taking it off, and be very consistent, so he does not get confused or get mixed messages.
Once you and he are very comfortable with you extending his wings and in general handling him al over his body, its time to try to put the wings thru the loops and tighten up the harness. Some parrots are very OK with this part, and others it takes awhile to graduate to this point.
It took Salty a whole year, of gradually increasing the steps above, to where he is OK to put it on. We still do the first excercise above almost every night during training sessions.