Hi, I think the suggestion you just got is great - i would have told you the same. Just one thing i would like to add: never try to calm him or to stroke him when he is in a fearful situation - ignore it - as hard as it is for you, i understand that, but that is the only way to show him that this is not a problematic situation for you. If he tries to hide behind you, do not let him. Try to be as relaxed as possible and as calm as possible.
Also try not to train too much or too long. As soon as you see that it is enough for him, let him have a rest - he needs it. Training can have a positive effect if it is short and clear - too long, too much ruins everything.
I wish you all the best!! If you have any further questions - just ask.
Greetings, Michael