Oh it is very complicated to earn his trust. I would suggest the African Grey Parrot handbook by Mattie Sue Athan. (have read two times) I found these links off of FB pages and they really helped me alot.
Welcome to Africangreys.com &
https://companionparrotonline.com/Member_Articles.html. They both have other links and resources listed.
I got my Grey about a month ago (to be here when my old english was dying) and we are now enjoying each other so much more after I did some reading. I had to learn their body language and how you can tell by looking at their eyes if they are stressed or happy.
One thing I will tell you is you will be bite, there is a reason for that, they are trying to determine that you are a worthy flock mate (security). If you are strong and do not react by pulling away they know you are ok. My first bite felt like a razor being pushed slowly into my finger. It hurt like a biatch! I slowly put her back into the cage with the step down command and then went and yelled. If you show weakness and over react (it's hard)they will see that as a weak flock member. I have a big perch that I roll up to the cage to let her out and play. They needs lots and lots of toys that they can play with and shread.
It takes a lot to earn their trust, as they are only 2 generations out of the wild, they just stopped importing them in the 90's.
Just take your time with him and approach them very relaxed, they are very perceptive and can sense if you are tense.
Right now she is very talkative and says good girl, pretty girl, hi, hello, how are you, and she has finally got the song sweet georgia brown down.Tons of sound effects, has my dog whining down pat. They have the intelligence of a four year old and the language skills of a two year old.
When she bite me it took me over a week to get my confidence back up to start trying to get her on my finger again. Everything I read was wait and avoid the same interaction to avoid them biting you again.
Try using a small perch you can use to have them step on, use the step up command, (hopefully they were taught that) didn't work for me but it may be worth a try. Patience is the key, if you force the issue they may feel very threatened and not trust you. NEVER NEVER yell at them, they will never forget and some more issues may develop.
Mine was allowed freedom around thier old house and we have to cage ours during the day so that caused some stress on her but I believe we are making great progress.
I hope this helped a bit.