I can retrieve user information when saving and closing my workspace BUT FROM A USER? from an Add-I

Hello.

Currently I need to pause when creating a user from the desktop agent, based on a custom field (the ID of the employee/user), I need to get it and go to a client system through a REST API to autocomplete some fields ( not all because some are manual). as I get data from an incident or a contact from an Add-in in C#, I can also retrieve user information when saving and closing my workspace BUT FROM A USER?. Failing that, I can create users by REST API.

I have been investigating these two options but I have not been successful in my search, any information you could provide me would be very helpful.