After I gave Mango some apple slices and grapes I left the room and went back downstairs to the Cockatiels and Mango was calling me and I went up to him and then I gave him a nice warm shower and he was so close to stepping up on my hand in the shower but then decided to retreat lol.But I like that he called me.

It's definitely a good sign!

I have to find a new method to tame him as I found out what im doing is negative as its forcing him to do something and he isn't being rewarded for it.

Desensitizing is a little bit negative but not very much, and sometimes there's no other realistic way to do it. It's acceptable if you do it gently. It would be unacceptable if you stuck your hand in the cage and left it there while the bird flapped around in a panic until it was too tired to keep on trying to escape. It's called flooding when you do something like that. But showing the bird your hand from a distance that doesn't make it too uncomfortable and then taking the hand away isn't harmful.

Birds are designed by nature to deal with not always being perfectly comfortable. Flock members argue with each other and compete for resources like the best bits of food, the best perching spots and the best nest spots, so they're not always completely happy with each other. When you come a little closer than he'd like and then back off, you're basically acting like a flock member. When you force yourself on him and make him do something that he doesn't want, you're acting more like a predator.

Do you have any ideas on something new I could try?