What can i do to make my tiel trust me better to help him sc the sheaths on his head and neck?

my atieal is a bird a many faces. one min he is singing and talking and just being a crazy bird. and the next min he is hissing and screaming. almost like he has Bi-Polar. now, he gets pin feathers allot on his Crest, head and neck. allot of people that have had atoos, macaws and tiles all said that their bird loved it when they would help take off the sheaths encasing the pin feathers (not the same as blood feathers). however my teal will have nothing to do with it. he will sit on my shoulder, perch on my finger, even play with my gles and tug at my hair. but when it comes to touching him he will have nothing to do with it. i got him second hand, well third hand technically. i don't know much about the original owners, however they people who we got him from never paid attention to him and neglected him. he wont ever be able to fly because the follicles for the flight feathers are damaged from really bad clipping and pulling. really , i just want to get him to trust me to where i can pet him. unless hes just going to be a no touch bird.