That is one very happy Amazon!
It is important to remember that Amazons have no switch between play and rough play. To them, its all play! As a result, they do love rougher play, so keep in mine not to push 'Pressure training' backwards. As Beak Pressure meets a give level, be prepared to say no (not loudly), take a quick break and get back in there.
I understand that you need to hold the smart phone to video this, so if you are doing what I'm suggesting, that's wonderful.
Playing with Amazons: It is important to use both hands. When an Amazon is holding on with one claw and the Beak and they elect to switch to the other claw - they will be holding on with only their Beak! It will be natural for them to increase the Pressure to maintain a hold until the other claw can get a grip.
I like to work with both hands. One hand playing and the other hand acting as a 'safety net' to support either your hand or the Amazon, if a problem occurs. Now, at first your Amazon will not fully understand what that hand is doing, since it commonly is very near by, but not involved. So, it will require a little practice. Once your Amazon picks-up on the other hand being a supportive 'third party' he will place little attention regarding it being there. He may also become a bit more lacks in using both claws as he will become somewhat dependent on that hand to come to his support or provide support when needed (which is wonderful).
You can also, use that hand to cradle his back to provide a platform for him to play from 'upside down!.
When you are providing scratches consider also using your thumb and finger to provide a means to contour the feather and smooth its ends, (from both sides, plus make skin contact. Starting from the skin to the end of the feather. We are not as talented as they are at working with feathers, but with a little effort, you will learn. Also, using both thumb and finger will allow you to 'comfortably' work both side of the Beak and cheek. Soft, light pressure will win you more time to do more!
NOTE: Single finger contact can be a bit more difficult than what we want to provided, since without an additional contact point (thumb or finger) we do not have much feedback.
You are making fantastic progress! As I stated: That is one Happy Amazon!
Enjoy!