This is a reverse engineering project. Occurs on the regulator wears a flexible button element. And it is impossible to buy it separately.
Wait! We can print it cheap!
This model can help replace a broken flexible button. Print from flexible plastic. I printed from Elastane D160. The thickness of the walls is adjusted to the flexibility of Elastane D160, it is a fairly soft material.The model requires support when printing.
Save your lives, breathe freely and enjoy!