How to automatically save a custom field at Open Cart 3

Hi.
I will provide you the steps I am doing so to be more easy for you to understand.
1) User open an account from the registration page
2) Opencart automatically login the user to the system
3) The user see the success page
4) My success page Is already integrate it with an external API
5) This external API respond back a userid
6) I want this userid to store it as a custom fields of my user.
Thanks a lot

Nobody? Especially this what I want to do is to update my custom field