Replace first value of string and append new value

Hi!

Im testing the demo version to see if what I want to do is possible with the pro plugin. I have Woo customers that I want to change the phone numer on, I want to add the country code.

Step 1. Search and filter users on billing country.
Step 2. Use regex to replace first 0 of billing phone with country code.

Im trying on the demo, but cant get the regex to work. Is this possible ad how would the regex work?

Regards,
Jerry