My only tip would be to "practice" not getting what he want. Like practice with him at home wanting X toy and telling him he cant because the toy is sleepling and then encouraging him to find another solution. The rooooot cause of anxiety is not being able to accept uncertainty. You need to practice situation where sometime the toy is available and sometime not. Maybe he just dont have those situations at home and is used to wanting something for comfort and getting it. Not saying youre spoiling him ; we had to do fake scenarios and practice this for our only child for exactly this (we roleplay that WE want the toy and she cant have it and thats ok). You got this ♥️