Custom Phone Format

Hi,

I would like change international phone format. The current one in cs-cart is expected to enter a country code. But, I would like to assign a constant country code fe.g. +31 ___ ________.
Is there any way to do it?
(note: I followed the this tutorial (https://docs.cs-cart.com/4.8.x/user_guide/users/customers/phone_validation.html) to figure out how to do what I want. But, this tutorial didn't work for me.)